Kaigaku (獪かい岳がく, Kaigaku?) is a supporting antagonist in the Infinity Castle Arc of Demon Slayer: Kimetsu no Yaiba. He is a demon affiliated with the Twelve Kizuki, holding the position of Upper Rank Six (上じょう弦げんの陸ろく, Jōgen no Roku?), replacing Daki and Gyutaro after their deaths. Kaigaku was a former Demon Slayer and Zenitsu Agatsuma's senior disciple under the former Thunder Hashira (鳴なり柱ばしら, Nari Bashira?), Jigoro Kuwajima. However, sometime during Hashira