Denji is an orphaned teenager burdened by substantial debts inherited from his deceased father. His resulting extreme poverty forced him to sell organs and work as a devil hunter for the yakuza alongside his companion, the dog-like Chainsaw Devil Pochita. Betrayed and killed by the yakuza, Denji was revived when Pochita merged with his body, becoming his heart and transforming him into a human-devil hybrid. This fusion restored his lost organs and granted him the ability to transform into Chainsaw Man by pulling a cord on his chest, manifesting chainsaws from his head, arms, and legs. Raised in poverty without formal education, Denji initially displays naivete, rudeness, childishness, and underdeveloped social skills. Underlying empathy drives him to aid others despite his own struggles. His early motivations revolve around simple desires: eating bread with jam and experiencing physical intimacy, like touching a woman's breasts. He accepts dangerous missions, such as rescuing Power's cat for the promise of fondling her chest, though he later finds such gratification fleeting. Joining Tokyo Special Division 4 of the Public Safety Devil Hunters under Makima's supervision, Denji forms significant bonds with colleagues Aki Hayakawa and Power. Makima exploits his emotional vulnerability, promising to fulfill his dreams if he helps kill the Gun Devil. During this time, Denji grapples with fears of losing his humanity, particularly when his hybrid form unleashes a ruthless, bloodthirsty persona in battle. Witnessing the deaths of Aki and Power—the latter killed by Makima—shatters his will to live, allowing Pochita to take full control. After Makima's betrayal reveals her as the Control Devil, Denji defeats her by exploiting a loophole in her regeneration: he dismembers and consumes her, nullifying her immortality through an "act of love." This victory leaves him responsible for Makima's reincarnation, Nayuta, whom he adopts as his younger sister. He resigns from Public Safety but continues fighting devils as a vigilante while enrolling as a student at Fourth East High School. Post-Makima, Denji's desires evolve to include lavish goals like daily steak breakfasts and multiple girlfriends. He grows more reckless, openly hinting at his Chainsaw Man identity to gain attention—leaving his school ID at battle scenes or confessing to classmate Asa Mitaka. His actions are also financially motivated; he scams homeless individuals by reselling used cigarettes and allows people to use him as a "chair" for money. Secretly, these efforts fund Nayuta's education and lifestyle, revealing a matured sense of responsibility. Despite this growth, he remains emotionally scarred, suffering nightmares about his patricide and habitually biting his finger when recalling Makima's influence. Denji's combat relies on his hybrid physiology. Transforming requires pulling his chest cord and sufficient blood; low blood results in partial transformations. He can extend or retract his chainsaws at will and regenerates injuries by consuming blood, granting near immortality unless his heart is destroyed. He displays tactical ingenuity in battle, igniting himself to weaken light-sensitive foes, creating a clone to deceive Makima by removing his own heart, or severing his brain to resist mental attacks. His interactions with women show mistrust stemming from repeated betrayals, yet he treats them with comparative kindness and respects their consent, contrasting his aggression toward men. This complexity defines his dynamic with Asa Mitaka and the War Devil Yoru; he protects Asa during conflicts but struggles with her dismissal of his Chainsaw Man identity. Recent events, including Nayuta's apparent death and his imprisonment by Public Safety, trigger further emotional breakdowns, highlighting unresolved trauma and self-loathing.