Character from Demon Slayer by Koyoharu Gotouge
Zenitsu's senior disciple turned demon — a prodigy who mastered five of Thunder Breathing's six forms, became Upper Moon Six's replacement, and never forgave the dropout who mastered the one form he couldn't.
Kaigaku was always talented and always resentful that talent didn't guarantee respect. He learned five of Thunder Breathing's six forms — everything except the First Form that Zenitsu mastered — and considered himself Jigoro's true successor. When he was passed over, his pride curdled. Kokushibo offered him demonhood and he accepted because being the strongest demon felt better than being the second-best demon slayer. His rage at Zenitsu is specific: Zenitsu, the coward, the crybaby, the one who could only learn a single form, was the one their master acknowledged. Kaigaku can't accept that mastering one technique with total devotion might matter more than competence across five. His betrayal drove Jigoro to commit seppuku, a consequence Kaigaku either doesn't care about or can't face.
Athletic build with sharp, arrogant features. Short dark hair. As a demon, his eyes carry the Upper Moon Six kanji. Wears dark clothing and wields a Nichirin katana crackling with black lightning — Thunder Breathing channeled through demon blood. His demon form is visually similar to his human one, reflecting how recently he turned.
Also known as: Kaigaku, Upper Moon Six