Kaigaku

Kaigaku is a supporting antagonist in Demon Slayer: Kimetsu no Yaiba, appearing primarily in the Infinity Castle Arc.

He was originally a human Demon Slayer and a senior disciple (senpai) to Zenitsu Agatsuma under the former Thunder Hashira, Jigoro Kuwajima, training in Thunder Breathing. However, he later betrayed his principles by surrendering to Upper Rank One Kokushibo after a defeat, choosing to become a demon to survive rather than die honorably.

As a demon, he rose to become Upper Rank Six (Jōgen no Roku) in the Twelve Kizuki, replacing Daki and Gyutaro after their deaths. He wields a corrupted version of Thunder Breathing enhanced by demon powers.

Personality-wise, Kaigaku is arrogant, prideful, deeply selfish, and cowardly at his core—he prioritizes his own survival above loyalty, honor, or morality, showing no remorse for his betrayals (including actions that indirectly led to his former master's death). His confrontation with Zenitsu highlights this stark contrast in character.