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 the anime series Hanyō no Yashahime.

History
Shortly after Setsuna and Towa were born in Kaede's village, Sesshōmaru took them away and left them to fend for themselves as a rite of passage. Setsuna and Towa lived together in the woods until they were four years old where Towa got pulled into a time portal to the present after the two of them were separated during a forest fire. At some point afterward, Setsuna suffered from some sort of anterograde amnesia due to the dream butterfly, which causes its victim to neither have dreams nor sleep.

Years later, Setsuna made her way back to the village around the time she was an adolescent, apparently having been informed Kaede would look after her. Kaede would then leave her in the care of Kohaku, who had become the leader of the newly formed yōkai taijiya, where she was trained in their ways.

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 aunt-in-law Moe; a small soft spot in her otherwise stern demeanor.

Physical Description
As a fraternal twin, Setsuna’s appearance is different from her twin older sister. Setsuna is a young woman of average height with fair skin. She has long black hair with a hint of red, tied in a high ponytail, with violet eyes. Unlike most of the other hanyō—including her paternal uncle Inuyasha—Setsuna shows no other visible physical indication of being a half-demon, 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 undone, her takes on the typical appearances of a hanyō: her nails become claws, canines become sharper, she displays some of the marking Sesshomaru displayed, and her ears become pointy.

Setsuna is typically seen wearing the standard demon slayer outfit. Her version consists of a navy kimono-like skin-tight jump suit, along with dark violet armored plating 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 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 Sesshomaru. She also wears dark purple boots with lavender trimmings and matching white fur near the top.

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

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 his 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.
 * Nagitanajutsu: Unlike her sword proficient father, Setsuna's main form of combat is a nagitana. She is extremely well-versed in utilizing it in close-range combat, able to fend off various high-speed strikes from a Hitokon-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 nagianta. 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 a inu-hanyō, Towa possesses an incredibly sensitive sense of smell, able to detect a human/demon's presence and/or whereabouts even at far distances.
 * 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: Setsuna can neither fall asleep nor have dreams due to having her dreams eaten by the Dream Butterfly. This resulted in her childhood memories falling to total amnesia. She claims this helps her stay alert in the warring age. Its implied even Modern Era sleep medicine can't do anything for her; despite there existing pretty strong medication to induce sleep. It evens works as an immunity to Yotsume's Dream Gazing spell. In addition, it made her immune to the New Moon weakness of other half-demons.
 * Venom Resistance: Inherited from her father, Setsuna is resistant to liquid poisons whilst her sister Towa is resistant to poisonous gases.

Weapons

 * Kanemitsu no Tomoe: Setsuna's primary weapon. A naginata with a golden handguard 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.
 * Senpū-jin: 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.
 * Muretachi no Tsubame: By slashing the air, Setsuna can unleash a barrage of green yōkai energy in the form of swallows towards her opponent.
 * Yadori Ga no Tsuki: 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.
 * Short Sword: Like most demon slayers, carries a sword in her waist as a secondary weapon.
 * Golden Rainbow Pearl: Setsuna possesses the golden Rainbow Pearl inside her right eye.
 * Slayer potion: As a demon slayer, Setsuna keeps various anti-demon potion in her elbow guard.
 * Violin: Setsuna was given a violin from her half-aunt-in-law, Moe Higurashi.

Weaknessess

 * 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.
 * Venom Gases: Setsuna is vulnerable to poisonous gases produced by demons.

Relationships
Sesshōmaru is her biological father. Having never met him, Setsuna treats her father as simply a stranger. She refuses the Tree of Age's request to fight Kirinmaru, believing that this is Sesshomaru's responsibility and not hers.
 * Sesshōmaru

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 Yume no Kochō has caused Setsuna to lose all memories of her.
 * Towa

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 Hitokon, Setsuna was willing to kill her despite having access to an anti-demon potion, even stating that anyone who opposes her is an enemy.

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.

Towa honestly wants to help Setsuna get her dreams back. But Setsuna is not interested and regularly refuses to help.

Towa wanted to save the monk Juan when he was possessed by the cat yokai while Setsuna and Moroha tried to kill him. Towa said that she grew up in an era of peace, that is where she will return and that is why she believes in peace. Even after Towa successfully saved Juan, Setsuna was upset and told her that this attitude will one day kill her.

Inuyasha is her paternal half-uncle. Like Inuyasha, Setsuna is a hanyō (half-demon).
 * Inuyasha

Kagome Higurashi is her half-aunt-in-law. She first learns of her through the Higurashi family.
 * Kagome Higurashi

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.
 * 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.

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 Hitokon, 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

Kohaku is Setsuna's leader in the demon-hunting band based in Kaede's village. She eagerly seeks new quests from him.
 * Kohaku

The nekomata Kirara is one of the few beings whose company Setsuna enjoys. Kirara is often seen carrying Hisui, but helps other yōkai taijiya as directed by Kohaku.
 * Kirara

Trivia

 * Setsuna is the only known demon slayer who is not a full human.
 * Despite being an Inu-hanyō like her uncle Inuyasha, 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'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.
 * Setsuna can be rendered unconscious with blows to the head but only briefly; she recovers within a moment when a rock hits her in episode 8.
 * 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. Its also possible that it is a side-effect of the Dream Butterfly taking her dreams.