Akaza

The Infinity Castle is an alternate dimension consisting of endless wooden rooms, halls, and moving corridors. It possesses a warped direction of gravity, allowing demons to stand upright, upside down, or perpendicularly on the walls, or move in physically impossible directions. Its unusual structure and layout as Nakime's Blood Demon Art allows any structure within to shift at her will, though the castle additionally also seems to move on its own. During the final assault against demons by humanity, the castle held many notable battles. These included Doma's clashes with Shinobu, Kanao, and Inosuke, Tanjiro and Giyu battling Akaza, Muichiro, Genya, Sanemi, and Gyomei facing Kokushibo, Zenitsu's duel with Kaigaku, and Mitsuri's and Obanai's skirmish with Nakime. Throughout the castle, numerous lesser demons, all having comparable strength to the Lower Ranks, were also present. These demons were sent to attack anyone, including the rest of the trapped non-Hashira Demon Slayers, as part of Muzan's plan to exhaust them for him to kill more easily. Akaza: Akaza is a major supporting antagonist of Demon Slayer: Kimetsu no Yaiba. He is a demon affiliated with the Twelve Kizuki, holding the position of Upper Rank three. Akaza was a headstrong, stubborn, and battle-crazed social Darwinist who enjoyed fighting, especially against strong Demon Slayers. He purposefully drew out fights to savor every moment of it; the Upper Rank tended to become enthralled whenever he was hit by a powerful opponent, not due to masochism but out of a genuine admiration for their skills. Akaza always complimented his opponents when they unleashed powerful techniques or landed blows on him, usually remarking that their techniques and swordsmanship were magnificent and intriguing. Akaza looked down on anybody he deemed weak, so much so that his skin would crawl at the sight of them. He genuinely respected those who were strong in his eyes, demanding to know their names.