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, replacing Daki and Gyutaro after their deaths.

   Kaigaku was a former Demon Slayer and Zenitsu Agatsuma‘s senior disciple under the former Thunder Hashira, Jigoro Kuwajima. However, sometime during the Hashira Training Arc, Kaigaku encountered and lost to Upper Rank One, Kokushibo, and surrendered to him to save his own skin, thus becoming a demon and later a member of the Twelve Kizuki.

As a human, Kaigaku is a muscular young man of average height with black hair and turquoise eyes. After becoming a demon, he gains many demonic traits like four black flame-like markings on both sides of his cheeks, fangs, pale skin, black sharp nails, and pointed ears. By becoming a member of the Twelve Kizuki and rising to the position of Upper Rank Six, his eyes are etched with the kanji of “Upper Rank” and “Six”.

   Kaigaku is usually seen wearing a black kimono with a blue obi over his Demon Slayer uniform that has yellow flame-like markings near the chest area. He also wears multiple necklaces on his neck and wrist with green colored strings that hold together blue magatama-like pendants that were yellow in color when he was human.