Kohaku

is Sango's younger brother. He is also a Yōkai Taijiya, like his sister and father, from the Village of Demon Slayers. He was manipulated by Naraku through most of the series, kept alive only by the Shikon Jewel shard in the back of his neck.

History
When he was still an infant, his mother died and his sister always took care of him along with their father (who later died).

During the story
He was killed by a demon posing to be a castle's lord during one of the Yōkai Taijiya's missions and was made to kill every Yōkai Taijiya that was there. He is later revived by Naraku as a human puppet and has a Shikon no Tama shard embedded in his back to keep him alive and under the control of Naraku without memory of what he had done. But recently, Kohaku has somehow got his memory back and still takes orders from Naraku to get to Naraku's heart. Kohaku, at first before being slain, was inexperienced with his weapon, a kusarigama (a sharp sickle on a chain). He then becomes a rather advanced wielder with the power of the Shikon Jewel shard. He encountered his sister a few times not long after being under Naraku's control and at first he was unable to recognize her at all, although her face does seem familiar to him. Early on, Kohaku was ordered by Naraku to kill Kagome, but he was prevented from doing so.

After Kagura dies, he hopes that he can find redemption for himself by traveling with Kikyō, and remains by her side until she tells him he must leave her to keep his shard pure. Saved from Byakuya by the timely arrival of Sesshōmaru, Kohaku forms a friendship with Rin (whom he had met before) and helps to protect her. In chapter 529, Kohaku's jewel shard was removed but surprisingly, he did not die or wither away. This was due to Kikyō's light releasing the jewel shard and remaining in Kohaku's body, as explained by Kagome.

Later life
In the last chapter, Kohaku goes with Kirara and a new demon-slaying weapon which Tōtōsai made for him, becoming a Yōkai Taijiya that helps people. When Tōtōsai asks him if he will visit his sister Sango, he replies that he will not, since the house is getting too crowded.

Personality
Kohaku is a humble and kindhearted boy who cares for his family and is very close to his sister Sango. When Naraku controlled his mind he was forced to kill everybody including his own father, it left him in a state of shock. Naraku then used the guilt-ridden Kohaku as a pawn and puppet for his dirty work. Though Kohaku was a gentle boy, he was easily manipulated by Naraku to commit terrible acts because of his weak heart. He desired to to forget the memories of killing his father and companions and allowed Naraku to erase them so his mind would be more at ease. After several encounters with Sango and her comrades as Naraku's pawn however, he begins to remember his sister and his life as a demon slayer. The memories bring back his extreme guilt and sorrow, thus, he decides to kill Naraku and redeem himself. Kohaku is also very self-sacrificing about his own life compared to others, such as giving his own life to save Kagome, who had been taken hostage by Naraku. Kohaku's greatest desire is to face his father and comrades in the afterlife with an apology and be forgiven.

Sango
He is very close to his sister; though he was brainwashed by Naraku who resurrected him from death. Kohaku meets Sango and realized her as his older sister, though he hid himself from her. Once he regains his memory, Kohaku is determined to kill Naraku secretly without letting Sango know. He feels great guilt for causing Sango much emotional pain and and believes he is unworthy of life. By the Final Act, he begins to feel the desire to live once more and redeem himself.

Naraku
Though he willingly obeyed Naraku for much of the series, Kohaku always despised him for manipulating him and causing him to kill his father and comrades and wound not only Sango but countless others. Over the course of time, Kohaku's memories return and he becomes determined to kill Naraku and avenge his loved ones killed by Naraku and also to redeem himself for being used as a killer. In the Final Act, Kohaku betrays Naraku and escapes with Kagura's help and from that point Naraku hunts Kohaku for his jewel shard. Once Kikyo uses Kohaku's shard as part of her plan to destroy Naraku, Kohaku becomes a major threat to his great enemy and Naraku is forced to plan carefully when dealing with him.

Rin


After abducted by Kagura, Rin met Kohaku in the shrine. They soon befriended each other. In fact, Rin lost her entire family who were slaughtered by thieves and Kohaku struggled to recover his memories when Naraku controlled him. At first their relationship went bad when Naraku ordered Kohaku to kill Rin in front of Inuyasha, Kagome and Sesshōmaru, but he refused to. They encounter each other a second time in a cave on Mount Hakurei. Kohaku protected Rin from the emerging demons, but also urged her to escape before she was killed. Later, he joined Sesshōmaru and Jaken after Kagura and Kikyō's death. In the later of the series, Kōhaku becomes protective of Rin, thus having their friendship continuing well.

Kikyō
His first meeting with Kikyo as an enemy, Kohaku was unsure of Kikyo until he fled from Naraku and refused staying with Inuyasha's group. He came across Kikyo and begged her to use his life to destroy Naraku, thus, redeeming him of his guilt and sins. He was not phased by her warnings her plan would lead to his death, he even accepted it gladly. During their journy together, Kohaku begins to have respect and concern for Kikyo, even worrying when she puts herself in danger. Kohaku mentions his main purpose for staying with Kikyo to Sango as, Kikyo's presence calms his spirit and he feels as if sins are cleansed and redeemed around her. When Kikyo dies, Kohaku is guilt-ridden he could not protect her and is resolved to carry out her mission to destroy Naraku with his shard.

Inuyasha
Inuyasha has tried to protect Kohaku from death several times including a time with Sango and with Sesshōmaru. Inuyasha is determined to keep Kohaku alive for two reasons: he does not want Naraku to get what he wants (i.e. the Sacred Jewel shard in his back), the taking of which would lead Kohaku's death and also because he knows that Sango will be grief-stricken if her brother dies. Kohaku comes to respect Inuyasha greatly.

Miroku
Miroku, like Inuyasha, has desperately tried to save Kohaku several times during their meetings, even risking his own life in the process. Because he is in love with Sango, Miroku is aware what Kohaku's death would do to her and thus does everything in his power to protect his life. Kohaku later acknowledged the monk's bravery during his possession by Magastuhi as well as his sister's love for Miroku. As Naraku is destroyed in the Final Act, Kohaku asks Miroku to take care of his sister for him. By the Final Act, he clearly accepts Miroku.

Sesshomaru
Kohaku joins Sesshomaru after Kikyo's death and stays as part of his group a great part of the Final Act. Kohaku is respectful and admiring though wary of Sesshomaru and spends much time guarding Rin when Sesshomaru cannot. Kohaku forever is not afraid to beg Sesshomaru to spare others' lives, an example being when his sister Sango nearly killed Rin trying to kill Naraku. Kohaku is the first to offer an excuse for her and desperately tries to convince Sesshomaru not to kill Sango in anger. This shows that he very much cares for and would do anything to protect his sister, much like she did for him and is in essence a role reversal (ie Sango settling down as a housewife and her brother becoming more of the dominant protector)

Quotes

 * "I want to remember... that girl... myself... and everything. But..."
 * "What's this? This feeling... it's... scary... Like there's something I shouldn't remember...!"
 * "Sister!"
 * "No sir, I'm not a ninja".

Trivia

 * The new Kusarigama that Kohaku received from Totosai is extremely reminiscent of the corrupted weapon that he had as Magatsuhi's body.
 * As stated by Sesshōmaru's mother, Kohaku can't be revived by Tenseiga because his life has already been unnaturally prolonged.
 * Akiko Yajima voiced Kōhaku in the Japanese version, and she also voiced Yura.
 * In the early episodes of the anime, the jewel shard that kept Kohaku alive was in the middle of his back. Towards the end, it was at the top of the neck.