Aki Hayakawa is a Public Safety Devil Hunter whose childhood in Hokkaido was shattered when the Gun Devil killed his parents and younger brother, Taiyo. This trauma drove him to join the Devil Hunters at sixteen, fueled by an obsessive quest for revenge against the Gun Devil. On the surface, he appears stoic, serious, and blunt, often clashing with more chaotic personalities. Beneath this cold exterior, however, he is kind, softhearted, and deeply affected by the loss of comrades, openly grieving for those he has lost. His dedication to his work is absolute, and he initially views devils as nothing more than disposable tools, believing they deserve no sympathy. Over time, his growing bonds with Denji and Power—two devils he lives with and cares for as a surrogate family—begin to outweigh his thirst for revenge. He becomes a beleaguered but responsible older brother figure, cooking for them and protecting them. His relationships with his former partner Himeno, his superior Makima, and the Angel Devil also shape him profoundly. Aki’s capabilities come from contracts with several devils: the Fox Devil, whose head he could summon with the word “Kon” until he lost that ability through reckless use; the Curse Devil, which manifests as a nail-like sword that can inflict fatal damage after three strikes but drastically shortens his lifespan, leaving him with roughly two years to live; and the Future Devil, which resides in his right eye and grants him a few seconds of precognition, allowing him to predict attacks at the cost of showing him visions of his own death. Beyond these powers, he is a highly skilled swordsman and hand-to-hand combatant. Despite his growing desire to protect his new family, his loyalty to Makima is exploited, and he is ultimately forced into a contract that transforms him into the Gun Fiend. In his final moments, while hallucinating a simple snowball fight, he is killed by Denji, and his spirit finds peace reuniting with his brother.