Akaza, Upper Rank Three of the Twelve Kizuki, serves Muzan Kibutsuji directly as a powerful demon. His appearance features a muscular build, green-tinged white skin patterned with thick blue lines like criminal tattoos, short bright pink hair, and yellow eyes with blue sclera resembling cracked glass; the kanji for "Upper Rank Three" is etched into his irises. He typically wears a sleeveless dark purple-pink haori cut off at the waist, baggy white pants secured by a blue rope belt, and pearl anklets, preferring bare feet. Over two centuries prior, he lived as the human Hakuji, possessing black hair, pale blue eyes, and three black criminal tattoos on each forearm, often dressed in a dark blue-gray yukata. Raised in Edo's slums, he stole to buy medicine for his sick father. Following his father's suicide from shame over Hakuji's crimes, Hakuji faced banishment from Edo. He encountered martial arts master Keizo, who offered him shelter and training in the Soryu Style. Hakuji nursed Keizo's daughter Koyuki back to health, eventually becoming engaged to her and set to inherit the dojo. This period ended when a rival dojo poisoned Keizo and Koyuki. In retaliation, Hakuji killed sixty-seven members of the rival dojo, attracting Muzan Kibutsuji. Muzan transformed him into a demon, erasing his human memories and bestowing the name Akaza. Akaza exhibits a battle-crazed obsession with strength and a firm belief in Social Darwinism, despising perceived weakness while respecting formidable opponents. He often prolongs fights to savor combat, commending skilled techniques and demanding the names of strong adversaries to honor their prowess. He repeatedly offers powerful humans the chance to become demons to preserve their abilities, killing them if they refuse, as with Kyojuro Rengoku. Despite his brutality, he adheres to a self-imposed rule never to consume or kill women, a remnant of his human life linked to Koyuki. His relationships with fellow Upper Ranks are antagonistic, viewing Doma and Kokushibo as rivals. Akaza's abilities stem from mastering the Soryu Style martial arts, augmented by demonic power. His combat skills include sensing "Fighting Spirit," enabling him to predict opponents' moves and detect weaknesses. His Blood Demon Art, "Destructive Death," unleashes shockwaves manifesting as energy projectiles or concussive forces, augmenting his physical strikes. As an Upper Rank demon, he possesses immense durability, regenerates near-instantaneously (even regrowing his head after decapitation), extraordinary speed, and tactical intellect refined through centuries of combat. His willpower allows him to defy conventional demon weaknesses, surviving beheading by Nichirin blades through sheer resolve. During the Infinity Castle Arc, Akaza battles Tanjiro Kamado and Giyu Tomioka. Tanjiro's perspective that the strong should protect the weak unlocks Akaza's repressed memories of his human life. He recalls promises to Keizo and Koyuki, realizing he dishonored Keizo's teachings by using Soryu Style for murder. Consumed by remorse for his actions as both human and demon, he loses his will to fight. Accepting defeat, he ceases regeneration after Tanjiro decapitates him. His final act is a smile of gratitude toward Tanjiro for restoring his memories, followed by his spirit dissolving into reunion with his loved ones.