Setsuna

"It doesn't matter if I dream or not. The lack of it has never caused me to suffer."

- Setsuna pondering on the fact she can't sleep

is the deuteragonist and one of the title characters in Hanyō no Yashahime. She is the youngest daughter of Sesshōmaru and Rin and the younger fraternal twin sister of Towa Higurashi.

History
Shortly after Setsuna and Towa were born in Kaede's village to Rin, Sesshōmaru took them away and left them near the base of a tree in a forest to protect them from Zero, who would target them due to a prophecy of their grandfather stating it will be half-demons that would slay Kirinmaru, (since the Shikon Jewel had been disappeared granted a wish by her half-aunt Kagome Higurashi seven years prior after the battle with Naraku) with Jaken placing a protective barrier around the Tree to keep them safe from Zero. Setsuna and Towa lived together in the woods until they were 4 years old, when Towa got pulled into a time portal to the present after the two of them were separated during a forest fire caused by Homura under Zero's order, with her father unable to intervene lest Zero kill Towa and Setsuna herself. After the forest fire, Setsuna first met with her father's vassal Jaken, stating that he was glad that she's okay, he looked around about for her sister, and she told him that Towa has disappeared. Jaken put her within a barrier and went in search of help. After learning of the progression of the silver scale curse afflicting Rin, Jaken returned with a chrysalis of a Dream Butterfly to use on the infant to help save her mother. She was crying for the loss of her sister when he returned and placed the chrysalis on her, and guided by A-Un and Jaken she was taken to the Hanyō Hidden Village.

Shortly afterwards, Setsuna arrived at the Hanyō Hidden Village where she was cared for by a hanyo named Shiori for six years before heading off to the village she was born. Setsuna's stay in the village didn't last long and she soon returned to the hidden village. When an army of demons led by Gaga Gozen attacked the half-demon village, Setsuna fought to defend Shiori, who had lost her demon powers during a total solar eclipse. During the eclipse, Setsuna's daiyokai blood awoke for the first time when she was restrained by Gaga Gozen and broke loose, tearing her assailant to pieces and then attacking the monk Miroku, who managed to subdue her with assistance from Shiori. He later applied a seal to her to prevent future rampages.

Afterwards, Shiori convinces Setsuna to return to Kaede's village and upon her return, it was decided that she would train under Kohaku, who had become the leader of the newly formed yōkai taijiya.

During the story
Setsuna would reunite with her twin four years later, ten years after the separation in the fire, and met her half-cousin Moroha. Setsuna and Moroha would meet when clashing with each other and later Mistress Three-Eyes. Mistress Three-Eyes stole the Gold Rainbow Pearl from Setsuna's eye and the red one from Moroha, transforming into a more powerful form.

A portal opened and sucked all three of them into the modern era where they met the Higurashi family that had adopted Towa. Setsuna didn't remember Towa and rejected her attempts to get close. Towa helped them kill Mistress Three-Eyes and Hitōkon, and Setsuna and Moroha stayed with the Higurashi family at Sōta's, Moe's, and Mei's apartment for three days.

Moroha made a deal with the demon that resided in the Tree of Ages, Ne no Kubi. When the trio passed through the Tree of Ages to return to the feudal era, they encountered the Spirit of the Tree of Ages that took the form of the late priestess Kikyō. The spirit asked them to kill the demon Kirinmaru, who was attempting to twist time, but that would also mean killing Sesshōmaru, who was, unknown to her at the time, her father.

Setsuna and Towa refused and were thrust into a confrontation with Ne no Kubi, and destroyed it for good. They returned to the Feudal Era and were drawn into conflict with the Shikyō that served under Kirinmaru. The first was Tōkotsu and his son Jakotsumaru, who were dispatched by Moroha and Setsuna laid Tōkotsu's soul to rest with a prayer she had learned from Miroku years ago, though she didn't know who he was.

The girls next encountered a village that was controlled by cats. There, they met a monk named Juan, who would later revealed to be possessed by an evil cat demon spirit. Setsuna believed they'd have to cut down the monk to stop the cat demon, but Towa figured there must be another way. Setsuna admonished Towa for her soft heart, but Towa found a way to use her weapon to absorb the cat demon's yōkai, and free Juan without hurting him.

With the aid of Moroha's associate Takechiyo, Setsuna and Moroha set out to find and rescue Towa when she went missing. They fought Fubuki, who worked for another member of the Shikyō named Kyūki. Moroha destroyed Fubuki, and she and Setsuna drove Kyūki's servant Yotsume away. They followed Yotsume to Kyūki's hideout where they fought him. Yotsume used a dream spell on Moroha, Towa, and Takechiyo; but Setsuna was unaffected due to having no dreams, and she effortlessly destroyed Yotsume.

The girls then went to confront Kyūki, but Towa and Moroha's demon powers were still sealed, leaving Setsuna to battle Kyūki alone. Kyūki transformed into her true form and kept absorbing Setsuna's attacks with her rainbow pearl. While hiding, Moroha and Towa realized Towa could absorb the demonic energy of attacks. Towa let Kyūki attack her, and then tried to impale Kyūki and the pearl in her mouth with her sword. The attack wasn't strong enough, and Towa was knocked back while Kyūki took the sword with her tail.

As Kyūki attacked, Setsuna pushed Towa out of the way and was struck in the head by a rock. Dismayed, Towa unleashed her full demon power and caused the sword to sever Kyūki's tail and return to her. Towa blasted Kyūki with the Sōryūha. Kyūki was defeated and returned to her normal form before dying at Riku's hands. After the battle, Towa placed a bandaid on Setsuna's injury.

Personality
Setsuna has a calm, unflappable personality much like her father, Sesshōmaru. Born as the half-demon daughter of a powerful yōkai, Setsuna appears to be somewhat resentful of her status as a hanyō due to the fact that she is not as powerful as some full-fledged yōkai.

As a child, Setsuna was cheerful and carefree but as she grew into adolescence, she became aloof and cynical. She seems to have no qualms in using violence against her opponents, as she firmly believes killing enemies is a means to survival. Her indifference towards others extends towards her own father, whom she feels is unworthy of being referred to as her father due to her never knowing him, and her own twin sister when they first meet.

However, she respects Kohaku and Hisui as they work alongside her as demon slayers. She also respects Kaede for looking after her. After meeting the Higurashi family, Setsuna develops a familial bond with them and is grateful for their hospitality.

During her travels, she also met a traveling monk, whose teachings she remembers well. This reflects in her attitude towards her foes, with whom she frequently seeks absolution for troubling them with battle.

Setsuna seems to not care about her Dream Butterfly curse, and is irritated by Towa's concern and soft-heartedness due to the influence of the modern era, up to the point where she forces the latter to "Cut down those ideals along with the Ghost Cat!" to which Towa refuses, reminding her of the time she spent there, and of Towa's promise to return after she restores Setsuna's memories and ability to sleep.

Setsuna is protective of the violin given to her by her half-aunt-in-law Moe; a small soft spot in her otherwise stern demeanor. She also regularly patrols the half-demon village she grew up in to protect them from demons that seek to harm the inhabitants. She also tries to avoid killing them whenever possible.

After regaining her memories from the Dream Butterfly, Setsuna's cold exterior melted away. She snapped Towa out of her demon form by shedding tears in front of her sister as she called her "sis" the second time since she was dying during her second battle with Kirinmaru, even apologized and embraced her. She also finally acknowledged Moroha as her friend and teared up in happiness when Moroha was reunited with her parents.

Physical description
As a fraternal twin, Setsuna's appearance is different from her older twin sister. Setsuna is a young woman of average height with fair skin, she's a bit taller than her older sister. She has long black hair with two red streaks, one on each side of her head, tied into a high ponytail by a white ribbon, and purple eyes.

Unlike most of the other hanyō—including her paternal half-uncle—Setsuna shows no other visible physical indication of being a hanyō, such as dog ears or elongated nails or canines, allowing her to fully pass herself off as a human. It is later revealed the lack of hanyō traits is due to a seal Miroku placed on her. When the seal is first seen undone in Episode 13, she takes on the typical appearances of a hanyō: her nails become claws, canines become sharper, she displays some of the magenta markings that Sesshōmaru displayed, and her ears become pointy. During her full demon state forced by Zero, her sclera becomes red, she gains a violet crescent moon marking on her forehead and a pair of orchid butterfly wings, and her body emits a green aura. Even after returning to normal, she retains a dark crimson marking on her right arm.

Setsuna is typically seen wearing the standard demon slayer outfit. Her version consists of a navy kimono-like skin-tight jump suit, along with deep violet armored plating with pale lilac accents on her chest, waist, left shoulder and elbows. The elbow guard serves as a place to store small-scale demon slayer equipment. She also wears a pale lilac hadajuban undershirt, and a lavender sash around her waist to carry a short sword.

Like her father, Setsuna has a large white fur over her right shoulder, which is split in two tails near the end. However, it is shown to be a piece of clothing rather than a part of her body like Sesshōmaru. She also wears deep violet boots with lavender trimmings and matching white fur cuffs.

As a child, she walks barefooted and ties her hair in a low bun with a light yellow hair tie. Her bangs on her left are also longer, partially covering her eyes. She also wears a blue kosode with a pink sash. Before she first meets Kaede, she lets her long hair run down freely and wears her large white fur around her neck as a scarf. During her time in modern Tokyo, Setsuna wears a long royal blue dress with sapphire heels, absent the aforementioned fur.

When she was born, Setsuna had short black hair with some strands of red and was wrapped up in a lavender blanket.

In Towa's dream, Setsuna wears a cyan sleeveless dress over a white middle-sleeved shirt, and her ponytail is tied by a white-furred hair tie instead. She also wears a pink bracelet along with Towa.

During the ending theme Transparent World, she wears the "Princess" long sleeve shirt, light blue shorts, socks with sandals.

When posing as Princess Aiya, Setsuna wears the princess' coat and kimono, with the fan on her obi. Her hair is tied with a white ribbon in a low ponytail and wears pink lipstick and common tabi (socks).

During the nights of the New Moon, Setsuna's hair almost grows to feet-length, the same as her step-grandmother, and her eyes take on a more brown hue to their color as her mother's. Her hair reverts to its original length when the moonless nights come to an end, and her eyes regain their purple coloring.

Back at the modern era through the Windmill of Time, Setsuna made a new look in the winter, as she wears Ms. Higurashi's lilac coat, her large white fur returns to go around her neck like a scarf, and it has a green cloth to cover the blade of her naginata with a dark gray strap for it.

During the ending theme Anaaki no Sora and in Episode 48, Setsuna wears a yellow colored kimono with lavender colored cloud signs on it with a white fur on her right shoulder just like her casual outfit also with woven sandals.

Powers & Abilities
Setsuna is a powerful yōkai taijiya, tapping into both her training as a demon slayer and her natural abilities as a hanyō. This, combined with her alert, no-nonsense personality, makes Setsuna an incredibly dangerous opponent.

As a hanyō, Setsuna cannot fully tap into the powers granted by her demonic blood, putting her at a disadvantage compared to a full-fledged yōkai. However, it is revealed in Episode 13 that Miroku placed a seal on her to keep her demonic blood at bay. Nevertheless, Setsuna is still shown to be far stronger than most yōkai. She was able to single-handedly fend off a Rainbow Pearl-empowered Mistress Three-Eyes, and likely would have defeated her had Moroha not interfere.


 * Like her father, Setsuna has claw-like fingernails. She can also scratch with her claws and release a potent poison at the same time to melt her enemies. Though she normally applies it through her claw strikes, she can also spray the acid from her claws or transfer it into her punches. Her poison is strong enough to melt rock or bone; a mere human or yōkai will melt in an instant. If her poison is taken in internally, it will remain inside and be in effect for a long period of time — even in those with demonic power. However, Setsuna can only activate this in her full-yōkai form.
 * Generation: Like her father, Setsuna can generate two thin, whip-like strands of yellow-green demonic energy from her fingertips in order to aid her, which she had first subconsciously activated in her unstable demon form.
 * Naginatajutsu: Unlike her sword proficient father, Setsuna's main form of combat is a naginata, just like Janis with her Akanemaru. She is extremely well-versed in utilizing it in close-range combat, able to fend off various high-speed strikes from a Hitōkon-possessed Towa before going in the offense.
 * Enhanced Physical Abilities: Being a hanyō, Setsuna’s physical abilities are far superior to the average human. She can fall down from a considerable height unscathed, a feat she already accomplished during childhood, as well clearing vast heights with a single jump. Setsuna also possesses incredible acrobatics and dodging skills, able to perform various back-flips and long leaps. Like her father, she moves with grace and elegance. As a child, she can push her sister Towa several meters through the air with one hand thrust. As a teenager, she is able to destroy a good portion of the ground with one swing from her naginata. Her speed is equally impressive, able to sneak behind Moroha and catch her off-guard despite the latter’s incredible sense of smell.
 * Enhanced Sense of Smell: Being an inu-hanyō, Setsuna possesses an incredibly sensitive sense of smell, able to detect a human/demon's presence and/or whereabouts even at far distances.
 * Affinity with Buddhist Spells: Since she had a seal from Miroku with his Buddhist powers, she learned it from him as to banish Tōkotsu as she chant, "'Meet an arat, then slay the arat. Meet your parents, then slay your parents. Know that the light to your path lies therein." and her sister Towa uses her demonic energy blade of the replica of Kikujūmonji to rest in peace.
 * Accelerated Healing: When Setsuna was injured in the arm fighting Tōtetsu, she said it would heal quickly. In fact, the wound was gone after a few minutes. It should be noted, however, that she was a full demon at this time, so it is unknown how quickly she heals as a half-demon.
 * Music Composer: Setsuna remembers when Rin hummed a tune while she was still pregnant of her, which is one of her few early childhood memories.
 * Violinist: During her time in modern Tokyo, Setsuna learned to play the violin from her half-aunt-in-law, Moe Higurashi. Despite having just learned it recently, Setsuna is proficient enough for Moe to praise her as a prodigy.
 * Sleep Deprivation : Due to having her dreams eaten by the Dream Butterfly, Setsuna can neither fall asleep nor have dreams. This resulted in her childhood memories falling to total amnesia. It's implied even modern era sleep medicine can't do anything for her; despite there existing pretty strong medication to induce sleep. Despite this, the condition has given Setsuna several advantages. She is immune to sleep inducing spells as well as the New Moon weakness of other hanyōs. Being unable to sleep also allows her to stay alert in the warring age. This came to an end when Sesshōmaru cut the Dream Butterfly at the bottom of Mount Musubi since her choice was to save her mother.
 * Venom Resistance: Inherited from her father, Setsuna is immune from venom-based attacks, such as venom water.
 * Flight: When Setsuna was in her full demon state, she gained a set of purple butterfly wings which enables her to fly. However, at this time she was possessed by the Dream Butterfly. It is possible that she can no longer do that.
 * Sacred Tree of Ages portal teleportation: Setsuna has briefly entered the Sacred Tree of Ages via Mount Musubi's barrier. In Episode 36, Setsuna tells the Spirit of the Tree of Ages to let her inside to see her mother Rin, and the spirit gives permission to her as Setsuna goes through the Sacred Tree of Ages to enter inside the tree. In Episode 40, Setsuna goes through the Sacred Tree of Ages for the second time, along with her sister Towa for the first time as their father Sesshōmaru's haku is draining.
 * Spiritual Sight: Setsuna has the unique ability to see the spirit of the Windmill of Time, Akuru.
 * Cold Immunity: Setsuna can stand very low temperatures as seen in Episode 14, when she, her twin sister, Kirara and Goro where not affected by the icy cold in the mountains, like her father and grandfather. That turns out to be a demonic power because when she turns into a human, she then suddenly freezes.

Attacks and Techniques

 * By slashing the air, Setsuna can unleash a barrage of green yōki in the form of swallows towards her opponent. After the creation of the Yukari no Tachkiri, it is much wider, stronger and leaves more physical destructive damage than ever before at strikes at longer distance and angles.
 * By spinning the naginata rapidly above her head, she can create a massive cyclone of wind, sucking enemies into it and inflicting major damage. It can also function as a projectile attack by spinning the naginata towards her opponent.
 * At one point, she attacked with a fiery bird from a distance during her third battle against Kirinmaru. How she realized her naginata had this attack is unknown.

Weapons

 * Kanemitsu no Tomoe: Setsuna's former primary weapon. A naginata with a golden hand-guard and white fur tassel that matches her outfit's color scheme. It appears to be a highly valuable weapon, as Moroha initially expresses interest in obtaining it. It also acts as a means of sealing her demon blood.
 * : By spinning the naginata, Setsuna can summon a swarm of resting moths that releases sleep spores, causing subjects to fall asleep. However, it has no effect on those who've been cursed by the Dream Butterfly. After the Dream Butterfly was cut by Sesshōmaru's Tenseiga, it is unknown what effect it would have on her without the Dream Butterfly.
 * Yukari no Tachikiri: Setsuna's new and current primary weapon. Forged by Tōtōsai during Setsuna's revival, it is made of the original blade, Lapis Lazuli, Quartz and Volcanic Soil. Similar in build to the Kanemitsu no Tomoe, the blade is larger and sharper, replacing it's two air/water related attacks from Setsuna's childhood. It can also freely cut objects and bodies, whether bodily or immaterial of any kind. It would have strong enough to cut the thread of fate tethering Rin and Zero's lives and lift the fatal silver-scale curse.
 * Wakizashi: Setsuna carries a wakizashi in her waist as a secondary weapon; hers is shorter than the ones used by most demon slayers.
 * Gold Rainbow Pearl : Setsuna possesses the Gold Rainbow Pearl inside her right eye.
 * Slayer potion: As a demon slayer, Setsuna keeps various anti-demon potion in her elbow guard.
 * Dagger : When she was staying at the hidden half-demon village, Setsuna received a tantō (traditional Japanese dagger) to aid in her training to use her powers. It ended up broken when clashing with Kanemitsu no Tomoe which at the time was used by Gaga Gozen.
 * Blood Blade: A sword that is dwelling within Setsuna's right arm that is harness directly into her Yukari no Tachikiri.
 * Penetration: The blade glows bright green and then pierces through demonic barriers.

Weaknesses

 * Demonic Blood: When the enemy is too powerful and can't defeat, Setsuna is willing to change into a full-fledged demon. While undoubtedly more powerful in this form, her demon blood overwhelms her into a whirlwind of rage whose sole purpose is destruction. However, knowing this form is very unstable, she requested Miroku to seal it with his spiritual power and only be unsealed when the situation is dire. When she was younger, Setsuna had first succumbed to the blood when the moth demon, Gaga Gozen, was attacking a human state Shiori and several half-demons.
 * Poison: Despite having inherited her father’s venom immunity, Setsuna still remains susceptible to some poison-based attacks, such as poison mist.
 * Sedatives: Due to having a strong sense of smell, certain scents can knock her out. Miroku used a sedative used by demon slayers to make her unconscious whilst she was in full-demon form.
 * New Moon: After transforming into a human ever since the curse was removed, Setsuna doesn't change that much. The features she gains is that her eyes turn brown, just like Towa. Another feature is that her hair grows long enough to her feet, like her late step-grandmother's. Throughout the transformation, Setsuna feels the cold since her demonic powers are temporarily neutralized as well as great fatigue since the curse has been removed. The only thing that has never changed was her mokomoko.

Family

 * Sesshōmaru

Sesshōmaru is her biological father, who had both her and Towa grow up in a forest with no one other than each other to protect them both from Kirinmaru’s forces (or more specifically, Zero’s), although neither Towa or Setsuna seemed to mind not knowing their biological parents as they were far more content with each other. In the current time, a teenage Setsuna treats her father as simply a stranger as she hadn't met him yet. She refuses the Tree of Age's request to fight Kirinmaru, believing that this is Sesshōmaru's responsibility and not hers. The two officially met when Sesshōmaru himself arrived during the half-demons’ battle with Kirinmaru, intervening the process by knocking his daughters out and battling in their place. Afterwards, however, Setsuna did not give much thought to him, although she appeared to be curious as to his intervention. A while later, Sesshōmaru sensed in the wind that his youngest daughter was losing control of her demon self. After Setsuna’s demise, Sesshōmaru appeared to gift his eldest daughter Towa his broken Tenseiga, and despite appearing detached, it was hinted he intended for Towa to resurrect Setsuna, showing his care for them both despite Setsuna’s disinterest.


 * Rin

Rin is her biological mother and the one who named her and Towa. Despite deeply loving her newborn daughters, Rin permitted Sesshōmaru to take them on the night of their birth to protect them from Kirinmaru and Zero. Setsuna lived alongside Towa with no knowledge of either of their parents in the forest, perfectly content with life and neither seemed hindered by her lack of parents. As such, Setsuna appeared to have no interest in learning of her mother because she hadn't heard of her either, since her lack of knowledge of her family does not hinder her. It is later shown that Setsuna's dreams and memories (which were stolen by the Dream Butterfly) were transferred to Rin to keep her in her incessant sleep in order to slow down the silver scale curse from spreading. As a result, Rin sealed away Setsuna's memories to spare her the pain of losing Towa in the fire, a fact she was unaware of back then.

However, after meeting her mother for the first time at Mount Musubi's barrier and hearing from the Tree of Age's how she is sealed, Setsuna resolved to free her. The violin tune Setsuna plays originates from a lullaby sung to her and Towa when Rin was still pregnant with them.

After the final bout with the multiple colored threads of fate and the Grim Butterfly, Setsuna, along with her sister Towa, finally embraced with their mother Rin.


 * Towa

Towa is her older twin sister, whom she lived happily with in the forest until the age of 4. Setsuna and Towa grew up together and used to always be together when they were young. Setsuna had a loving and inseparable bond with her older sister and used to call Towa “Sis (Onee-chan)”. Initially, Setsuna was extremely close to her older sister, to the point that she pushes her away from a falling tree to save her. Unfortunately, the influence of the Dream Butterfly has caused Setsuna to lose all memories of her.

When the two reunited again ten years later, Setsuna treats her with indifference and refuses to believe that they are related. She even tries to attack Towa, telling her to use her strength to prove that they are sisters. After Towa was possessed by the Hitōkon, Setsuna was willing to kill her despite having access to an anti-demon potion, even stating that anyone who opposes her is an enemy.

After returning to the Feudal Era, Setsuna continues to remain as cold and distant to Towa as ever. She regularly reacts with contempt whenever Towa attempts to bond with her. Having never considered her inability to sleep as damaging, Setsuna does not share Towa's desire to find the Dream Butterfly and regularly refuses to help in her quest.

The difference in upbringing further disconnects their bond. Having lived in the war-heavy feudal era, Setsuna considers Towa naive and emotionally weak. She criticizes her for being able to sleep after her first yōkai encounter, as well as calling her foolish for saying she doesn't want to cause any more trouble for the Higurashi family. When they travel back to the feudal era, Setsuna continuously warns Towa to keep her guard up, out of basic concern to not see the newcomer perish in an unfamiliar era. She also considers Towa's pacifistic nature as a hindrance. After the monk Juan was possessed by a cat yōkai, Setsuna insists on killing him and tells Towa to discard those ideals. Even after Towa successfully saved Juan, Setsuna still insists that this attitude will one day kill her. Instead however, it only lead to her demise during her second battle with Kirinmaru (albeit briefly).

As the two continued to spend time together, Setsuna gradually became more civil and tolerant towards Towa, especially as she began to remember their past. Besides being willing to play the violin to her upon request, she also began engaging in casual, and sometimes heartfelt, conversation with her. She also displays a certain protectiveness over her sister, often coming to her aid during battle, along with expressing concerns over her strange symptoms during her new moon transformation. Nevertheless, she still remains annoyed by Towa’s attempt to bond with her.

As time passes however, Setsuna continues to open up to Towa. Eventually she reaches the point where she is able to tell Towa personal things about her past and was even able to smile and laugh in her presence again. She even becomes protective of her, as she wanted Towa to stay hidden during the next new moon when her powers left her, though she was pushy about it, criticizing her for not listening after she wandered off. This shows that Setsuna is slowly becoming a more social and caring person towards her older sister, though she is still not ready to admit it. It was hearing her sister's voice that enabled Setsuna to regain control over her body when she was consumed by her demon blood.

As Setsuna was dying, she referred to Towa as "Sis (Onee-chan)" for the first time since age 4 in which the curse had been briefly broken.

As Setsuna was rushing to Nanahoshi's mansion, she blocked Towa's attack on Zero and tells her to calm down and says if she kills her she'll also be killing their mother. Towa, who is in her uncontrollable state however, says that she doesn't care about that and swears to get Zero back for everything she has done. Setsuna then slaps her, and says that their mother had given her the Dream Butterfly, which was holding onto all of Setsuna's memories. Once her mother returns the memories that were sealed away, it was revealed that Setsuna blamed herself for not keeping up with Towa when they were escaping the fire. Upon showing the truth to her transformed sister, Setsuna's relationship with her long lost twin was restored as she tearfully embraced her sister.

After Towa lost her kon by the Zanseiken the first time, Setsuna became more concerned about her sister's life as she told her along with Moroha never to use the sword again, in which Towa does so later on by saving Rion.

Later on while dealing with the multicolored threads of fate alongside with Moroha, Setsuna warned Towa not to use the Zanseiken as her kon will be stolen once more if she does. Towa however tells Setsuna and others to carve their own fate by letting them know that it's the only way. After Towa used the Zanseiken to save Rion from her past and Osamu Kirin and collapsed, Setsuna was left extremely worried that there was no way of bringing her back. After Towa granted Rion use of her body to bid farewell to her father Kirinmaru, Rion returned her twin to life, much to her joy.

Moroha is her paternal half-cousin whom she met when she confused her with a demon who was attacking a village. Setsuna initially thought Moroha was a full demon and was surprised that she could use sacred arrows. She quickly came to view her as an annoyance, due to interrupting her battles and her constant remarks of her being a hanyō and even teasing and calling her "Setsu (Setsuna-chan)".
 * Moroha

During their stay in the modern era, Setsuna begins to view Moroha in a better light, finally calling her by name and seeking her for advice in combat. However, she still remains annoyed and unimpressed at Moroha's sillier antics.

When Moroha was fighting Kirinmaru as Beniyasha, she expressed concern for her when Kirinmaru threw Moroha to the ground. She reminds Moroha that they're friends and she shouldn't have to face Kirinmaru on her own.

When she witnessed Moroha reunite with her mother, she tears up in happiness that they're back together.

When Towa sacrificed herself by using the Zanseiken to save Rion from her past and Osamu Kirin, both of were worried that they wouldn't see their warm-hearted relative ever again until she was miraculously saved by Rion. Both were highly relieved to see her brought back to life once more.

Moe Higurashi is her half-aunt-in-law. During her short time in the modern era, Moe Higurashi taught Setsuna how to play the violin, which she quickly mastered. The two got along well, with Setsuna praising her as a good teacher and telling her that she'll continue to play the violin.
 * Moe Higurashi

Mei Higurashi is her half-cousin-in-law, whom she saved from being killed by Mistress Three-Eyes. She appears to be in good terms with her, willing to engage in casual conversation with her cousin. When she was initially possessed by the Hitōkon, she was originally planning to cut it from her eye. But remembering Mei's smile, along with thanking Setsuna for saving her life, causes her to simply use the anti-demon potion on her instead.
 * Mei Higurashi

Her half-aunt in law and the elder sister of Sōta, Kagome first met Setsuna when she was a newborn and Setsuna met her 14 years later at the Border of the Afterlife. Kagome was horrified when she heard that Setsuna was once murdered and then was amazed that Towa was able to save her with the broken Tenseiga. Setsuna watched Towa introducing Kagome her smartphone as well as showing her new sister-in-law and half-cousin-in-law.
 * Kagome Higurashi

Her paternal half-uncle and a fellow half-demon, Setsuna first meets Inuyasha at the Border of the Afterlife. Inuyasha was amazed while hearing that Setsuna was saved by her older-sister, Towa, who weld the broken Tenseiga and was able to revive her. Inuyasha is a lot more gentle and extremely supportive to his nieces in comparison to their father.
 * Inuyasha

Friends
She met the two half-demons when she was brought to the Hanyō Hidden Village as a child. They were both about their age and quickly became friends and did lots of things together. When Gaga Gozen attacked, the three of them fought to protect the village. Both were a little scared to see Setsuna as a pure demon, but quickly accepted it. When Setsuna left the village for good, they said goodbye to her happily and hoped to see her again. Even though they are no longer in contact, Setsuna probably still sees the two as her friends.
 * Fūta and Raita

Others
A monk who Setsuna met about three years prior to reuniting with Towa, Miroku was the one who placed a seal on Setsuna's demonic blood to prevent her from losing control after her first time going berserk. Miroku cares for Setsuna's well being; when Zero defeats him and steals his sealing ability, his first thought is to worry for the half-demon's safety, ordering his monk daughter Kin'u to her side.
 * Miroku


 * Kaede

The priestess whom Setsuna was under the care of for some time, she was also one of the few who witnessed her and Towa's birth. Kaede knew that Setsuna was Sesshōmaru's daughter, but for some unknown reason she didn't tell Kohaku and the other demon hunters. When Setsuna lived in the Hanyō Hidden Village for many years and then came to Kaede's village at the age of ten, the elderly priestess took care of her. When bandits attacked one day, Setsuna wanted to kill them, but Kaede stopped her before she could. Kaede didn't want Setsuna to fight and kill at such a young age, whereas Setsuna didn't see why she, as a half-demon, should have to respect human sensibilities. This led Setsuna to leave the village and return to Shiori. A few years later, however, she seems to have become more warm-hearted and to have accepted Kaede's words for herself.


 * Jaken

A loyal vassal to her father, Jaken acted as a caretaker to both her and Towa growing up. While she was crying for the loss of her sister following the fire that separated them, Jaken secretly put the Dream Butterfly chrysalis on her neck as he and A-Un took her to the hidden village for hanyōs, although he remained unseen the entire time, and presumably Jaken watched over her from afar. However, upon meeting him during the clash between Sesshōmaru and Kirinmaru, she doesn't remember who he is. After she and the others leave Mount Musubi with Rion, she met Jaken again, as the Dream Butterfly appeared, learning from him that the Dream Butterfly was being used to stall a curse placed on her mother by Zero. After she and the others, including Moroha's parents get out of the Border of the Afterlife, from the gate at the Lake of the Staff of Two Heads, as she and Towa enter the Sacred Tree of Ages, they meet Jaken with their parents as they heard from him that their father needs help. After Towa's kon has been drained, he told her that Akuru can be seen by the Dog Demon Clan. He told them to destroy the Grim Comet in the modern era by using the Windmill of Time in front of their grandmother's mansion.


 * Shiori

Shiori is a hanyō born from a human mother and a demon father just like Setsuna. After being separated from her older sister Towa in the forest fire, Setsuna was left alone. She sat by herself when A-Un and Jaken suddenly arrived, leading her to Shiori’s hidden village. Shiori soon welcomed Setsuna to stay in her hanyō village where many hanyō children were in Shiori’s care, including Fūta and Raita. Shiori had created a strong demonic barrier, protecting all hanyō children from any danger. Setsuna soon got used and adapted living in the village quickly and eventually learned to read and write as well as gathering food and hunting while hiding in the village from both humans and demons. Both Setsuna and Shiori care deeply about each other and Shiori was able to hold and calm Setsuna down when the village was being attacked by Gaga Gozen and Setsuna's demon form began awakening. Setsuna, just like her parental half-uncle Inuyasha, is incapable of managing her full demon powers. Setsuna has always been very thankful for Shiori’s hospitality and she stayed in the village until she became strong enough to leave and return back to Kaede's village where she was born. Setsuna then started to live in Kaede's village and became a yōkai taijiya alongside Kohaku and Hisui. Setsuna still comes back to the village whenever she can to save it from any possible yōkai as the village still means a lot to her, and Shiori watches from the cliffs, content to see one of her former villagers return.


 * Riku

After the battle with Kyūki, she meets Riku as an ally of Takechiyo and Jyūbei. In Episode 14, she along her sister Towa and her cousin Moroha were hired by Riku that he recused a beautiful woman Tamano from a corrupted mountain god Homura to take him down. Though Riku and her have had some interactions, usually when he has her and her companions fulfill a job for him, Setsuna seemed to have taken a fairly neutral view to him. Unlike Towa, whom Riku has taken a strong interest in, Setsuna doesn’t seem to consider Riku a friend, just an associate. For his part, Riku to respect Setsuna for being Sesshōmaru’s daughter, though he doesn’t take as strong of an interest in her as he does her older sister.

In Episode 21, when Riku hugs Towa, Setsuna orders him back, deeming him a threat since he has the same scent as Kirinmaru. Though Riku was slightly bothered by her interrupting his and Towa’s tender moment, he chose to make no move against her. Setsuna was later shocked when Towa gave Riku her Silver Rainbow Pearl, noting that it was a bad idea since Riku is a servant of Kirinmaru and that he could use the Rainbow Pearls for evil. This shows Setsuna now considers Riku to be an enemy. She is also seemingly aware that Riku possesses romantic feelings for Towa, though she disapproves of them due to him being a servant of their enemy.

In Episode 23, when Setsuna comes seeking revenge on Zero, Riku’s madam and the one responsible for her’s and Towa separation, she ends up running into Riku instead. Before their battle, Setsuna taunted Riku over his feelings for Towa, something that he didn’t deny. During their fight, Riku proved to be more than a match for Setsuna, with him blocking all of her attacks with ease. It is later revealed however, that Riku was going easy on her. When Setsuna later killed Zero with her blood blade attack, Riku was horrified and devastated by his madam’s death, but didn’t seem to bear any grudge against Setsuna after her father revived her with Tenseiga.

In Episode 24, she along her sister Towa and her cousin Moroha felt surprised that Riku stabbed Kirinmaru with his sword, in order to give them a better chance of defeating him or escaping. It is also revealed that Riku is aware that the only way to unlock Towa’s true potential is by killing Setsuna. Not wanting Towa to go through such pain, Riku secretly watches out for Setsuna. Not only did he hold back against Setsuna during their earlier fight, but he was even willing to lie to Zero in order to ensure that she wouldn’t be targeted. This shows that Riku, in truth, wishes to protect Setsuna, though this is more as to spare her sister from the emotional agony of her death rather than any attachment to Setsuna herself. Instead, Riku seems to hold Setsuna’s abilities in low regard, viewing her as too weak to protect Towa on her own and not really caring if she perishes or not.

When they meet again later, Riku aids Setsuna in killing three Oni attempting to kill her. Despite this, Setsuna warns Riku to stay away from Towa, still not trusting him around her sister. Riku, however, chastises Setsuna for not being strong enough to protect Towa, insisting that he will continue to be watching over her since she is incapable of it. Realizing that he genuinely he wants to protect Towa, Setsuna reluctantly lets Riku continue helping them. In gratitude, Riku leaves her a map to Bokusenō before disappearing.

As Riku knows Rion, Setsuna was uncomfortable to see Towa raising her voice at him that Kirinmaru can see and hear. After that, she sees Riku carries Rion onto the boat, before she starts to get sleepy again.

While they wait for the boss of the rock demon, she remembered Riku's verdict that she wasn't strong enough to protect Towa, grudgingly admitting he was right.

The daughter of her foe Kirinmaru, Setsuna was startled to learn of what Degenerate Age is about told by the Spirit of the Tree of Ages that her father is after the spirit named Akuru so he can move the Windmill of Time. As Towa hugs her terrified, Setsuna tries warn her not to be trusting. She sensed the thread of fate between Rion and her father that it has continued for 600 years. Rion tells her to sever it, but she has never done something like this. Rion tells her that if she do so, she'll be sent out into the afterlife, in which it'll stop Kirinmaru's tyranny. So Setsuna agrees, cut it and saw Rion's Dream Butterfly slash in half. After Towa gives Rion use of her body within the Grim Butterfly, she severs their thread of fate upon her request.
 * Rion

Enemies

 * Zero

Fearing the prophecy foretold by the Shikon Jewel of her brother’s death by a half-demon, Zero sought to assassinate Setsuna and Towa when they were infants. She was the one who sent Joka to kill them when they were babies, then put the Silver Scale Curse on their mother's neck and later ordered Homura to set fire to the forest which caused Setsuna to separate from her twin sister, Towa when they were four years old. Later, when the Towa and Setsuna began working together as teenagers and started eliminating the Four Perils, Zero became increasingly concerned and convinced that they may indeed be the ones destined to defeat Kirinmaru. This caused her to pressure her brother into dealing with them more seriously and was frustrated by his lack of action toward them. When Zero felt the time had come for her to deal with them herself, she undid the seal keeping Setsuna’s demon blood in check, causing her to go on rampage attacking friend and foe alike. As the seal was being broken, Setsuna recalled Zero’s eyes from her dreams as a child, before the forest fire causing her to realize that it was she who sent Homura to assassinate them. Upon realizing this, Setsuna developed an intense hatred of Zero, for not only being the cause of her separation from her sister, but also for undoing her seal and forcing her to injure Towa. Setsuna is now determined to kill Zero, wanting revenge for all the pain she has caused her. Since she did defeat Zero and was in a state of shock that her father Sesshōmaru resurrected her with his sword (originally her grandfather's) the Tenseiga, she didn't realize that Zero cast a spell on her mother Rin at first.

Kirinmaru

A great qilin demon who, according to the Tree of Ages, wishes to distort time. Setsuna was not interested in granting the spirit's request to slay Kirinmaru, believing that this is Sesshōmaru's responsibility and not hers.

Trivia

 * Despite being a half-demon like her paternal half-uncle, she and Towa seem to age at the same rate as humans. Rumiko Takahashi explains in Shonen Sunday Super that the reason Towa and Setsuna age normally is because half-demons age similarly to humans at first, but as they reach adolescence, their aging process slows down.
 * Setsuna retains her childhood kindness deep down; her solitary and combat-filled life simply pushed it into her subconscious, which is what makes her act against her cold-hearted logic.
 * Setsuna's name, like her sister Towa's, is a homophone with a time word, "Moment" or "An instant." This is probably an allusion to the fact that both sisters travel through time.
 * Despite being incapable of sleeping previously, Setsuna was still susceptible to being rendered unconscious.
 * Her demonic heritage likely compensates for inability to sleep, as a human would have died from little more than a week or two of no sleep. It's also possible that it is a side-effect of the Dream Butterfly taking her dreams.
 * It has become a gag that Setsuna tells Towa she's either too naive or too soft and when she dismisses Towa's quest for the Dream Butterfly.
 * When she turns into a full demon, her voice becomes feral. A snarl can be heard when Towa asks about her condition. Furthermore, whenever she turns into a full demon, she doesn't have the same stripes that Sesshōmaru has. Instead she has Tōga's stripes.
 * According to Towa's seiyū, Sara Matsumoto, Setsuna is represented by the flower Evening Primrose.
 * Unlike Towa who inherited their mother’s personality and their father’s looks, Setsuna inherited more of their mother’s looks and their father’s personality.
 * Setsuna is the first main character to die in the entire series; not until she however was revived by the Tenseiga in The Second Act's premiere which also marks her to be the first main character to be resurrected. Due to now having to wield a much more powerful naginata, it is most likely to be her only time dying in the first season finale since it was weaker before.
 * Her downfall was teased in BURN; not until her return was teased in Reborn.
 * According to the May 2021 issue of Animage, the song that Setsuna plays on the violin is not what Moe taught her, but rather it is something she remembers from her past. In the Second Act, it was revealed to be a lullaby sang by her mother, Rin.
 * According to her seiyū Mikako Komatsu, Setsuna thought that if she loses Towa basically means she loses herself.
 * Setsuna shares a few similarities with her half-uncle Inuyasha; both lost in combat with a moth yokai and were restrained by said foe, had their daiyokai blood awaken to save their lives, and reduced their enemy to shreds.
 * Setsuna also shares similarities with Maki Zenin from Jujutsu Kaisen:
 * Both have the same seiyū (Mikako Komatsu)
 * Their main weapons are naginata with a fur accessory.
 * They are both twins sisters except Setsuna is the younger twin and Maki is the older twin.
 * Both have enhanced abilities.
 * Both have powerful families.
 * Setsuna is the only half dog demon who doesn't have any white hair like Towa, Inuyasha, Sesshomaru, Toga and Sesshomaru's mother.