Kohaku

is Sango's younger brother. He is also a demon slayer, 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.

Personality
Kohaku is a humble and kind-heated 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 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 Kōhaku struggled to revoice his memories when Naraku controlled him. At first their relationship started out bad when Kōhaku was ordered by Naraku to kill Rin in front of InuYasha, Kagome and Sesshomaru, but he refused to. They encounter each other again in a cave in Mount Hakurei, Kōhaku protected Rin from the demons, but also urged her to escape before she was killed. Later, in the Final Act, he joined Sesshomaru and Jaken after Kagura and Kikyo's death. In the Final Act, their relationship goes on well when Kōhaku shows a caring and protective towards Rin. Kohaku and Rin became very close to each other. He became her best friend and protector.
 * Rin

Their relationship started out bad. Kōhaku slayed Kocho and Asuka by mistake after recovering his memories. After Kagura's death, he joined Kikyo in the Final Act who protected him for last shard keeping it pured and keeping it 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

History
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, Kōhaku has somehow got his memory back and still takes orders from Naraku to get to Naraku's heart. Kōhaku, 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.

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, Kōhaku forms a friendship with Rin and helps to protect her. In chapter 539, Kōhaku's jewel shard was removed but suprisingly, he did not die or wither away. This was due to Kikyo's light releasing the jewel shard and remaining in Kōhaku's body, as explained by Kagome.

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.

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 Kōhaku received from Totosai is extremely reminiscent of the corrupted weapon that he had as Magatsuhi's body.
 * As stated by Sesshōmaru's mother, Kōhaku 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.