Kohaku

Kohaku is Sango's younger brother.

Overview
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.

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 suprisingly, he did not die or wither away. This was due to Kikyou's light releasing the jewel shard and remaining in Kohaku's body, as explained by Kagome.

In the last chapter, Kohaku 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.

Trivia

 * The new Kusarigama that Kohaku received from Totosai is extremely reminiscent of the corrupted weapon that he had as Magatsuhi's body.