Kaigaku

left|thumb|Kaigaku's cowardice and treachery was on display even as a child. Though outwardly brash, haughty, and arrogant, Kaigaku was in fact cowardly and selfish. An orphan who grew up with nothing, he resorted to doing anything as a means to survive, like thievery and drinking from a puddle. His intense sense of self-preservation went so far as to sacrifice the lives of Gyomei Himejima and the other children under his care to save himself, showing that he would do anything if it meant his survival. This attitude was also evident during his time as a Demon Slayer; unlike those who join the Demon Slayer Corps, Kaigaku never developed a desire to slay demons or protect people. When he faced Kokushibo and realized how powerful he was, Kaigaku immediately surrendered to the demon, once again cementing his indifference towards making immoral choices if it will save him in the end. However, despite his disinterest in becoming a Demon Slayer for the greater good, Kaigaku showed a desire to gain status as a master swordsman, which was shown when, even as a demon, he chose to make his flesh katana reminiscent of his own Nichirin Sword. thumb|Kaigaku's hatred of being compared to Zenitsu. Kaigaku had a sense of hypocritical self-righteousness. He considered Zenitsu Agatsuma worthless for his perpetual cowardice and inability to master Thunder Breathing beyond the first form, and he was repulsed by the idea of succeeding Jigoro along with him. However, as he could not master the first and fundamental form himself, his perceived skill only amount to as much as Zenitsu's own, and his accusation of Zenitsu shaming Jigoro proved void when he himself ended up disgracing the former Hashira by becoming a demon. Furthermore, when confronted with the news of Jigoro's death, he only claimed his demise was earned for not believing he alone was worthy to succeed him. Kaigaku also possessed a twisted perspective of "right" and "wrong"; he believed that those who judge him right (i.e., say he was worthy) are good and those who judge him wrong and have a low estimation of him are evil. His inflated ego and superiority complex was most evident when could not stand the idea of sharing the position of Rumble Hashira with Zenitsu, and later accused Jigoro of favoring Zenitsu over him. In addition, when Zenitsu pointed out how Kaigaku could never master the first form and remarked that he pitied Jigoro for having such pathetic successors, Kaigaku immediately lost his composure and screamed at Zenitsu to not compare them to each other. left|thumb|right|Kaigaku proclaims that he will always side with those who know his worth. His myopic view of victory was such that if one hasn't died, even if they've suffered through hardships such as losing their home or drinking dirty water, or if they resorted to committing petty acts such as stealing money to survive, they haven't lost and can come back for victory someday. As a result, he deluded himself into believing he was the winner of his fight with Zenitsu simply because the latter was going to fall to his death, even though they both were going to die in that moment, and Zenitsu was for all intents and purposes the true victor, having beheaded Kaigaku before he could react and initiating his imminent demise. thumb|Kaigaku vindictive and uncaring of his teacher's suicide. Kaigaku was already spiteful and cruel as a human, as he constantly verbally abused Zenitsu by demanding that he leaves the Demon Slayer Corps and refusing to socialize with him when he tried to be friendly. However, becoming a demon revealed a much more unrestrained and psychotic side of him. Not only was he gleeful at the prospect of killing the junior he had long hated with his newfound power, but he sadistically expressed his satisfaction towards Jigoro's suicide with a large smile on his face, and repeatedly insulting his memory for not addressing his worth through how he perceived himself. His gleeful demeanor as a demon contrasted his personality as a Demon Slayer in training. During this time, Kaigaku was a depressed malcontent, who was in a constant state of dissatisfaction despite his great talent, promising future, and his life with individuals who valued him. The moments where he smiled or showed happiness were few and far between, and Kaigaku usually seen sulking by himself. According to Zenitsu, Kaigaku emitted a perpetual sound of discontent no matter the time; he compares his attitude to a "box-of-happiness" with a hole spilling out its contents, and it's implied that Kaigaku finally patched the symbolic box by his newfound strength as an Upper Rank demon. thumb|left|Zenitsu comparing Kaigaku's dissatisfaction to a box that never filled. Kaigaku was a foil to Zenitsu; while Zenitsu was a defeatist who was self-aware of his shortcomings and desperately wanted to improve upon himself, Kaigaku was a determined yet conceited egoist who barely reflected on his own cowardice, mi...

As a human, Kaigaku was a muscular young man of average height and pale skin tone. He had short, spiky black hair with two thick strands framing each sides of his face along with bangs at the front, and a pair of dull, cold teal eyes framed by thick, arched eyebrows. His expression was often unfriendly, and he had a semi-permanent snarl. While training under Jigoro, Kaigaku wore a black kimono with a white collar. It was worn loosely to expose his chest and his pendants, which are decorated with gold magatama beads and a blue string. When he became a Demon Slayer, Kaigaku wore the Corps' standard uniform, which consisted of a navy gakuran-style button-up jacket, with a stand-up collar and long sleeves, featuring silver buttons and a shirt pocket on the left breast, with the kanji for |Metsu}} engraved on the back of the uniform. Beneath the jacket, he wore a white long-sleeved collared undershirt. His uniform also included a pair of matching navy tattsuke-hakama held up by a white belt, tucked into a black fabric of cloth wrapped around his ankles. On his feet, he wore navy tabi socks and a pair of zori sandals with bright blue straps. After Kaigaku became a demon, he gained four navy blue flame-like markings on both sides of his cheeks, emerald green irises (originally colored cyan in the manga) with black sclera, elongated canines resembling 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 became etched with the kanji for |Jōgen}} on his right, and daiji of |Roku}} on his left. Kaigaku still retained his signature kimono, which was secured with a blue obi over a stylized version of his Demon Slayer uniform that has yellow flame-like markings near the chest area and an unbuttoned collar. His forearms are seemingly wrapped in white kyahan-like material, and he wears additional necklaces on his wrists. The magatama on his pendants are now blue instead of yellow, and have a light turquoise strings instead of blue.

Overall Abilities
Kaigaku overpowering Zenitsu with his Blood Demon Art-enhanced techniques. As a former Demon Slayer and the Upper Rank Six of the Twelve Kizuki, Kaigaku was a very powerful demon. This was supported by the fact that he received a larger portion of Muzan Kibutsuji's blood for him to turn into a demon than is usual, as users of Total Concentration Breathing are more resistant to the effects of the Demon King's blood. As a further testament to his strength, Zenitsu realized that Kaigaku had eaten a multitude of humans in the short period of time between Hashira Training and his encounter with him. However, he also acknowledged that Kaigaku only reached the bottom of the Upper Ranks by filling the blank spot left by Daki and Gyutaro, implying that his rank was out of convenience for Muzan and by merit of being stronger than the lesser demons infesting the Infinity Castle, rather than by legitimately matching his predecessors' power. Nonetheless, he overwhelmed Zenitsu for the majority of their fight and managed to severely wound him with his Blood Demon Art. Kaigaku was only defeated when Zenitsu unexpectedly used a self-taught form of Thunder Breathing to decapitate him. According to Yushiro, during Kaigaku's short tenure as Upper Rank Six, he had yet to master his techniques and abilities and likely would have immediately killed Zenitsu in a year's time. Even after dispatching him, however, Zenitsu would've been irreversibly damaged or even killed due to his encounter with Kaigaku anyways, if not from falling to his death down a chasm Kaigaku pushed him in, then from his Blood Demon Art posthumously decaying Zenitsu's body. Yushiro had to both rescue Zenitsu from his plummet, and administer a blood demon styptic to prevent further damage to Zenitsu's body, particularly to his face as the electricity nearly reached his eyes and blinded him.