Kaigaku

After being turned into a Demon, his human appearance completely changed, his skin became pale and gained wavy stripe-like marks on his face, his ears became pointed and his sclera was black, retaining the color of his human eyes, now bearing the distinctive kanji (陸上弦, Roku Jōgen (Sixth Crescent)) that credits him as the Upper Moon number six.

Her outfit underwent a major modification, now showing her in a black Kimono. Her Demon Slayer uniform also underwent certain changes, now having yellowish marks on its print, with a shirt with multiple buttoned cuffs under her old hunter uniform and various Magatama necklaces on her neck and wrists with a thick blue cloth tied to her waist; she also wore black tights fitted to her Hakama pants.

Kaigaku was a self-serving individual, with a rather unequivocal concept of morality, based on the concept of what is "right" and what is "wrong". A coward by nature, he valued his life above that of others, the most obvious example being how he was able to sell out his principles and betray the Demon Extermination Corps in order to save himself from death at the hands of Kokushibo when he saw that he could not defeat him, even agreeing to become a Demon at the first opportunity in order to save himself from a gruesome death.

Due to learning almost all of the Lightning Breathing's attack stances with the exception of the first, Kaigaku grew arrogant, believing himself to be the worthy successor of his master Jigoro Kuwajima. The fact that Jigoro made both him and Zenitsu Agatsuma his successors deeply annoyed him as he did not share the fact that Zenitsu, whom he saw as more than a pesky pest in his path of rising to power, was valued more highly than himself. However, this only serves to highlight Kaigaku's impatience and arrogance; his inability to use the first stance, the foundation of all the others, meant that his technique in the advanced styles could only go so far. This proves to be his downfall as while he was only able to increase his abilities after becoming a Demon, Zenitsu was able to develop an entirely new Seventh Form through dedicated training.

Due to his transformation into a Demon, Kaigaku's breathing techniques underwent a sharp increase in power, enough to fill the vacant spot of Upper Moon Six. However, Kaigaku was only just beginning to adapt to the changes that come with his transformation into a Demon, so his exact power was only just beginning to grow. Yushiro comments that if Kaigaku had been allowed to live another year, it's possible that Zenitsu would have died if they ever faced each other after that time.

Master Swordsman: As a former member of the Demon Extermination Corps, he possessed exceptional skills and great talent. His abilities were enough to make him the disciple of the former Roaring Pillar, Jigoro Kuwajima, and the possible next successor of the Lightning Breath. Lightning Breath (雷かみなりYo呼Yo吸きゅう¿ Kaminari no Kokyū ? ): This was the style he learned from his teacher, Jigoro Kuwajima . He barely knew five of the six existing attack stances of Lightning Breath, despite not learning the first stance, which was the most basic and the main one of the other attacks. Like Kokushibo , Kaigaku used his Demonic Blood Techniques to increase the power of his attacks allowing him to break the skin and burn the flesh of his opponent. In his visual appearance, all of his attacks had a black coloration. The stances he could perform were:

Second Stance: Thunder Ball (BuenoYoElBuenoSí 稲Sí魂Sí, , Ni no kata: Inadama ? ): It consisted of a series of five simultaneous attacks delivered in an instant.

Third Stance: Mosquito Lightning Swarm (参YoElBuenoSí 聚Pero蚊YoOSí雷Más, , San no kata: Shūbun Seirai ? ): He performed a spinning attack in several directions.

Fourth Stance: Distant Thunder (肆ElElBuenoSí 遠Más雷Más, Shi no kata: Enrai ? ): He launched a powerful long-range attack.

Fifth Stance: Burning Thunder (To me, The Good, Yes, Yes, More, Go no kata: Netsu Kairai?): Provided a cutting attack capable of breaking the skin and burning the flesh of his opponent.

Sixth stance: Electric Rain (PleaseYesTheGoodYes PleaseI轟Yes雷More轟Yes, , Roku no kata: Dengō Raigō ? ): It consisted of a series of attacks capable of breaking the opponent's body.

The person Kaigaku hates the most is Zenitsu Agatsuma, despite having been partners in the past, Kaigaku always felt hatred for Zenitsu for being too weak.