Itsuro Hazama, a former private detective, is mortally wounded while investigating cyborg-linked thefts tied to Biotechno Corporation and CEO Daigo. To cheat death, his consciousness merges with a cybernetic frame—inheriting the "8 Man" mantle from Hachiro Azuma, the original hero whose mind was mysteriously erased. The procedure, sustained by a specialized serum to prevent cognitive decay, leaves Hazama tormented by fragmented memories, chiefly his sister’s murder by corrupt officer Tony Gleck—a trauma that ignites his vengeful crusade.

Reborn as 8 Man, Hazama wields superhuman speed, strength, and shape-shifting prowess, meticulously replicating scars and features to preserve his human guise. His relentless tactics against Psycho Serum-addicted cyborg criminals draw condemnation from Sachiko Yokogawa, Azuma’s former ally, who challenges his moral compass despite his civilian protection.

Hazama’s vendetta intensifies when Gleck resurfaces as a cybernetic enforcer for crime lord Mr. Halloween, scheming to seize Biotechno. Their clashes trigger Hazama’s suppressed rage, overriding neural safeguards meant to curb emotional volatility—a flaw exposing the fragile symbiosis between his humanity and machine enhancements.

Struggling with identity erosion, Hazama adopts Professor Tani’s counsel to bury his past self, yet Sachiko’s scrutiny and echoes of Azuma’s legacy complicate his detachment. His capacity to mimic humanity—masking his cyborg nature—clashes with his lethal methods, framing a paradox of vengeance and preservation.

The narrative unveils Hazama’s body once housed Azuma, whose disappearance stems from an unresolved clash with the entity Kozuma, forging a cyclical legacy of sacrifice. Hazama’s journey ends ambiguously, his tenuous grip on humanity hanging amid spiraling violence and corporate conspiracies, unresolved yet inextricably bound to the 8 Man lineage.