Kohaku is the younger brother of the demon slayer Sango. Throughout the principal original series arc spanning episodes twenty-seven through one hundred and sixty-seven, he is the tragic puppet of the villain Naraku. He was killed on his first demon slaying mission but was revived by a Shikon Jewel shard embedded in the back of his neck, which erases his memories and bends his will completely to Naraku, keeping him alive only as a tool.

His background as a gentle, kind, and determined boy from the demon slayer village who admired his father and older sister is lost for the majority of this period. His personality becomes hollow and emotionless, wholly obedient to Naraku’s commands. His primary motivation is survival, enforced by the jewel shard, leaving him with no free will of his own. His role in the story is deeply painful; he is forced to fight directly against his sister Sango and the main group, serving as a constant reminder of Naraku’s cruelty and a key emotional weapon Naraku uses to manipulate the heroes.

The core relationship governing his character arc is with his sister Sango. Sango’s relentless drive to save her brother fuels much of her own story, while Kohaku is forced into a role of antagonism against his own family. Over the course of this episode range, scattered memories begin to return to him. When he fully recovers his memory, he becomes consumed by guilt and horror over being forced to kill his father and his fellow demon slayers. This trauma reshapes his motivation from simple survival to a deep need for atonement. He secretly rejects Naraku and becomes an inside agent, hiding his regained conscience to stay alive while seeking a way to destroy his master. He also forms a brief but pivotal connection with the wind sorceress Kagura, another being enslaved by Naraku, who entrusts him with the means to earn his freedom.

Kohaku’s development across these episodes is a painful journey from a soulless puppet to a young warrior actively fighting for his own redemption. His growth culminates in a conscious decision to sacrifice his own life to stop Naraku and free his sister from the conflict. In terms of abilities, Kohaku is a highly skilled demon slayer for his youth. He fights primarily with a large kusarigama, a sickle on a chain, and his physical prowess, speed, and strength are greatly amplified by the jewel shard in his back. He also possesses thorough knowledge of demon weaknesses and slaying techniques inherited from his family’s tradition. By the conclusion of episode one hundred and sixty-seven, Kohaku regains his life and free will. The Shikon shard is removed, and he chooses to spend his existence traveling alone as a ronin demon slayer, atoning for the actions he was forced to commit under Naraku’s control.