Kohaku
Kohaku is Sango's younger brother. When Kohaku turned eleven, his father told him that he must now put his training as a youkai taijiya (demon exterminator) to use and help the rest of his family (who are also demon exterminators) with their next mission; exterminating a Spider youkai who is tormenting a castle. Kohaku is scared, but he does not want to disappoint his father. Sango cheers him up by telling him he will be safe with her. However, during the mission something goes horribly wrong. Kohaku becomes a puppet of the Spider youkai, who has taken the form of the castle's lord, and kills his family. Sango sees the spider thread the yōkai is using to control Kohaku connected to the back of his neck and knows he is not himself. Sango tries to wake her brother up and a battle ensues. They fight until the false Lord orders them killed. Sango is wounded and Kohaku is released from the yōkai's spell. He rushes to aid Sango, only to be shot dead by the Lord's archers. It isn't until after this that the lord's son, Hitomi Kagewaki (whose body is later taken over by Naraku), realizes that his father has been possessed and kills him and order's that the yōkai taijiya be given a proper burial. It is later revealed that this was all setup by Naraku so that he could use the opportunity in which the youkai taijiya village's best warriors were absent to attack the village and take the shikon jewel shard there, then tell Sango that InuYasha was the one responsible so that she would attack him.
Kohaku is later on brought back to life by Naraku, and is kept alive by a shard of the Shikon no Tama lodged in his back. He remembers nothing of his past life and so, he becomes Naraku's servant. While Kohaku is Naraku's servant, his life is used as leverage to try and persuade Sango to steal the Tetsusaiga for him. Later on in the series, some of Kohaku's memories gradually return to him, but he still serves as a minion under Naraku. He is eventually instructed to deliver Akago to the castle of a noblewoman when her baby was stillborn. Naraku orders him to remain in the castle as a servant so that he may protect Akago from any potential threats. While protecting the castle from Princess Abi and her bird yōkai, he begins to fully regain his memory. Kohaku is then ordered to kill all the people he helped defend, so that he could retrieve Akago for Naraku, but in doing so he not only fully regains his memories—including those of the day when he killed his father and comrades—as well as his own will. Desperate to determine his identity and trying to stop himself from killing the noblewoman, he begins to cry before her. Sango arrives to stop him as Kohaku struggles to accept the surge of memories he is recalling. Kagura arrives to take him away; as they escape, he is able to fully assess his recovered memory, but keeps it a secret and decides that even at the cost of his own life, he will kill Naraku. After recovering his memory, he revisits his abandoned village in episode 163, to give honor to the taijiya that was slain by his own hands. Kohaku also runs into Kirara and remembers his childhood of his father and Sango, who he refers to as Ane-ue, while also battling some rogue youkai. At the end of this episode Sango realizes that she has a chance of seeing her brother and shouts his name while running towards the village. Kohaku decides to remain in the shadows and Sango narrowly misses him. After realizing about the secret flower garden, Sango now knows that Kohaku has his memories back.
After he inadvertently reveals he has recovered his memory to Kagura, the two form an alliance of sorts seeing as they are in a similar situation. They will defend each other, given that the other is the only one they can somewhat trust; in Kagura's final battle, she holds off Hakudoushi so Kohaku can escape and as she dies from Naraku's poison, Kohaku runs off in search of her, sensing Kagura is in some sort of danger.
Following Kagura's death, he joins Kikyo as he believes travelling with her will be the only way to redeem himself, full well knowing that she may sacrifice his life to complete the Shikon Jewel to defeat Naraku. He remains by her side until she tells him to separate from her for fear of being unable to keep his shard pure. However, he is nearly captured by Byakuya, and only a timely arrival by Sesshomaru saves him. Kohaku remains with Sesshomaru's group after this.
After Kikyo's defeat, Naraku succeeded in reuniting and corrupting all of the Shikon Jewel, except for the shard in Kohaku's body. Naraku has attempted to decapitate Kohaku to retrieve his shard, however a light from the shard prevents him from taking it. Because of this attempt, he has managed to openly betray Naraku. He has also managed to reestablished communication with his sister. It was recently discovered that using the Tenseiga to bring Kohaku back to life would not work. However Magatsuhi is not only able to touch it but corrupt the shard. Shortly after his birth, the detachment attacks Kohaku to get the shard, sending Kohaku into a coma immediately upon touching it. Sesshomaru tries to protect him, injuring his arm, but ultimately winning the battle when he obtains his new sword, the Bakusaiga, and regrows his left arm.
Kohaku remains in a coma for days, Kagome being unable to heal him due to her spiritual powers being sealed. While he sleeps, Magatsuhi takes possession of Kohaku's body and uses it to attack his comrades, poisoning both Miroku and Rin in the prosess. While battling InuYasha and the others, Magatsuhi reveals that ever since he touched Kohaku's shard, he has been reliving that day when he killed his father and his comrades. Although Magatsuhi is confident that doing this would shatter Kohaku's soul, Kikyo's light in Kohaku's jewel shard is able to help him esape from this endless nightmare, allowing him to regain control of his body. Magatsuhi attempts to take Kohaku's jewel shard by force, but is thwarted by Sesshomaru, who defeats Magatsuhi with his Tenseiga and Bakusaiga. Following his defeat, however, Naraku takes Kagome hostage, saying that he will release her if Kohaku gives him his jewel shard. Kohaku, ignoring the warnings of Sango and the others, agrees. As Kohaku is in clutches, Naraku tells him that even though he is going to die, he had already died on that day when he killed his father and the others with his own hands. But Kohaku rebukes him, saying that even though what he did was unforgiveable, Sango, InuYasha, and the others have shown him what significance his life has. It is then that Kohaku reveals an arrow of Kagome's that he had picked up earlier, and thrusts it into Naraku where the Shikon Jewel is. Kikyo's light inside Kohaku's jewel shard flows into Kagome's arrow and begins to engulf Naraku. As the arrow pierce through the armored shell protecting the jewel, Naraku is forced to let go of Kohaku, lest he be devoured by the purifying light. Naraku then flees, attempting to take Kagome with him, but due to is severely weakened state, InuYasha is able to rescue her with ease. As Kohaku rejoins the others, he realizes that he has now finally come to terms with his past. Now finally at peace with himself, Kohaku decides that he will continue to live on no matter what happens. Just then, some pieces of discarded body parts from the earlier battle with Naraku suddenly spring to life, and pierce through Kohaku's back and coming out through his neck, along with the Shikon Jewel. Having lost the one thing that sustained his life, Kohaku's lifeless body falls to the ground. However, Kikyo's light remains in Kohaku and sustains his life instead, at the cost of allowing Naraku to have and corrupt the final Shikon shard. In Volume 54, Kohaku first tries to kill himself but Sango says she needs him by her side.
During the final battle inside Naraku's new body, Kohaku helps to locate and assist Miroku and Sango who have been poisoned by Naraku's toxins. In the final chapter of the manga, set three years after the defeat of Naraku and the destruction of the Shikon no Tama, Kohaku is a full-fledged Demon Slayer. It is shown that Kohaku is now Kirara's master, having been given to Kohaku after Sango married Miroku and started a family. He meets with Totosai, who gives him a new weapon, and asks if he has visited his sister recently. He flies off with Kirara saying that her house is too crowded.
