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.

During the story
He was killed by a demon posing to be a castle's lord during one of the Demon Slayers' missions and was made to kill every Demon Slayer that was there. He is later revived by Naraku as a human puppet and has a Jewel of Four Souls 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 met his sister for sometimes at first he cannot remember her and tried to kill Kagome under Naraku's mind.

After Kagura dies, he hopes that he can find redemption for himself by traveling with Kikyo, 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 Sesshomaru, Kohaku forms a friendship with Rin and helps to protect her. In chapter 539, Kohaku's jewel shard was removed but surprisingly, he did not die or wither away. This was due to Kikyo's light releasing the jewel shard and remaining in Kohaku's body, as explained by Kagome.

Later life
In the last chapter, Kōhaku goes with Kirara and a new demon-slaying weapon which Totosai made for him, so he leaves and becomes a demon slayer that helps people. When Totosai 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 kind-hearted 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, leaving him in a slight state of shock. Early on Naraku used Kohaku not wanting to remember as a way to keep control over him. However, when his memories returned on their own, he did not seemed to be affected as severely as before.

Relationships
He is very close to his sister; though he was brainwashed by Naraku who resurrected him from death. Kōhaku 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. In the end, he became the maternal uncle to Sango's children.
 * Sango

After being kidnapped by Kagura, Rin met Kōhaku 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 started out bad when Naraku ordered Kohaku to kill Rin in front of Inuyasha, Kagome and Sesshomaru, but he refused to. They encounter each other again in a cave in Mt. Hakurei, Kōhaku protected Rin from the demons, but also urged her to escape before she was killed. Later, he joined Sesshōmaru and Jaken after Kagura and Kikyo's death in the Final Act. In the Final Act, Kōhaku became caring and protective towards Rin, thus having their relationship going well. They've been very close friends with each other. He became her best friend and like a protector towards Rin.
 * Rin

Their relationship started out bad. Kohaku slayed Kocho and Asuka by mistake after recovering his memories. After Kagura's death, he joined Kikyo, whom protected him and his shard, keeping it pure and away from Naraku until she was killed.
 * Kikyo

Inuyasha has tried to protect Kōhaku from death several times including a time with Sango and with Sesshomaru. 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 neck), the taking of which would lead Kohaku's death and also because he knows that Sango will be grief-stricken if her brother dies.
 * Inuyasha

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!"

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.