Kohaku is Sango's younger brother. When Kohaku turned eleven, his father told him that he must now put his training as a yōkai taijiya (exterminator) to use and help the rest of his family (who are also yōkai taijiya) with their next mission; exterminating a Spider yōkai 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 yōkai, 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 yōkai 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.