As a human, Kaigaku is a muscular young man of average height who has short, spiky black hair, with two thick strands framing his face, and a pair of dull, cold turquoise eyes framed by thick, arched eyebrows. He has an unfriendly face, that is always set in a semi-permanent snarl.
After becoming a demon, he gains many demonic traits like four black flame-like markings on both sides of his cheeks, elongated canines that resemble fangs, sickly pale skin, sharp blackened 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” ( Jōgen?) and “Six” ( Roku?).
When he was still human, who is still undergoing training under Kuwajima, he is shown to be wearing a black kimono with a white collar, worn loosely to expose his chest and his signature magatama-necklaces around his neck. When he became a Demon Slayer, he wore the Corps’ standard uniform consisting of a black gakuran-like jacket, a pair of equally black tattsuke-hakama pants held up by a white belt, tucked into white kyahan wrapped around his ankles, and a pair of tabi and zori