Demon Slayer Chapter 145

Demon Slayer Chapter 145, titled "Box of Happiness," delves into the tragic past of Kaigaku, revealing his encounter with Kokushibo and his subsequent transformation into a demon, culminating in an emotionally charged battle against Zenitsu Agatsuma and the revelation of a powerful new Thunder Breathing form. The chapter opens with Kaigaku recalling his encounter with Upper Rank One, Kokushibo, during which he believed it was not shameful to kneel before an overwhelmingly strong opponent. For Kaigaku, survival was paramount; as long as he remained alive, everything would eventually work out. He rationalized that societal scorn, forced humiliation, or accusations of theft were irrelevant—what truly mattered was his existence and the belief that he would someday achieve success. Kokushibo, observing Kaigaku's desperate will to live, offers him a chance to become a demon and gain immense power, drawing blood from his hand for Kaigaku to consume. He explains that if Muzan Kibutsuji recognizes his potential, he will be transformed. The process is lengthy, especially for stronger individuals, with Kokushibo himself taking three days to fully transform. To counteract the effects of Total Concentration Breathing, a significant amount of demon blood must be ingested, and only a select few are compatible with the transformation. Kokushibo warns Kaigaku to be grateful for the blood, threatening beheading if a single drop is spilled. Kaigaku vividly remembers the intense fear that gripped him as he consumed the blood, feeling his very cells screaming and crying, a chilling prelude to his demonic transformation in the thrilling narrative of the Demon Slayer manga.

In the present, Kaigaku, now an Upper Rank demon, scoffs at the thought of facing Zenitsu, whom he still considers a worthless coward, devoid of dignity or perseverance. He dismisses their shared past, recalling Jigoro Kuwajima's offer to make them both his successors and cursing his former trainer for comparing him to Zenitsu. Angrily declaring that both he and Zenitsu deserved to die, Kaigaku unleashes Thunder Breathing, Second Form: Rice Spirit, attacking Zenitsu with five consecutive slashes that wound his face. Zenitsu, observing the brutality of the consecutive attacks, sadly remarks that Kaigaku has devoured many victims, losing his ability to discern good from evil. Kaigaku retorts that he indeed knows the difference, asserting that those who recognize his worth are good, and those who don't are evil. He then uses Third Form: Thunder Swarm, expertly weaving around Zenitsu and inflicting further injuries. With Fifth Form: Heat Lightning, Kaigaku slashes and burns Zenitsu simultaneously, mockingly asking if he enjoys his blade, now infused with his Blood Demon Art. He follows with Sixth Form: Rumble and Flash, wounding Zenitsu throughout his body and gloating that his immense power, combining both burning and slashing, has allowed him to surpass the original Thunder Breathing style, further deepening the rift between them.

As Zenitsu falls, Kaigaku smugly remarks on their supposed fundamental differences. Zenitsu, however, recalls Jigoro's teachings: Thunder Breathing's foundation lies in mastering the first form. It was irrelevant if one could use other forms if the first was not perfected. He remembers Kaigaku's arrogant personality, even as a less proficient user, always dismissing those he deemed beneath him, yet ironically, this arrogance prevented Kaigaku from ever becoming a Hashira. Zenitsu understands Kaigaku's hatred for him, and despite reciprocating the sentiment, he had respected Kaigaku's relentless hard work. To both Zenitsu and Jigoro, Kaigaku was a special individual, yet nothing ever seemed to satisfy him. Zenitsu compares Kaigaku's heart to a box with a hole, constantly leaking happiness—no matter what went in, it could never be filled. Apologizing internally to Jigoro for their diverging paths, Zenitsu plants his feet along the wall to stop his descent. As Kaigaku watches in surprise, Zenitsu apologizes to him once more and unleashes Thunder Breathing, Seventh Form: Honoikazuchi no Kami, a technique he created himself, instantly decapitating Upper Rank Six. As he plummets, Kaigaku struggles to comprehend the attack, unable to perceive its speed or origin. He curses Jigoro for supposedly favoring Zenitsu by teaching him an exclusive form, but Zenitsu denies this, revealing that this seventh form was his own creation, one he had hoped to use to fight alongside Kaigaku. This climactic moment showcases Zenitsu's profound growth, his mastery over his breathing technique, and his heartbreaking dedication to a broken brotherhood, marking a decisive victory and a poignant end to their fated confrontation in the thrilling Infinity Castle Arc of the Demon Slayer manga.