Set in the frozen mountains of Japan, the series follows an unnamed, unnamed Japanese macaque whose snow troop banishes him after he integrates a gravely wounded American assassin named Bryce Fowler into their pack. The assassin, fleeing a botched cartel hit, soon perishes from his injuries. Driven by a desire for vengeance when
ruthless mercenaries slaughter his entire troop—including his beloved mate—the grieving monkey takes up Bryce’s guns. Fueled by primal rage and guided by the cynical, ghostly hallucination of Bryce himself, the primate embarks on a bloody, relentless quest for retribution that leads him straight into the neon-lit
criminal underworld of Tokyo.As the simian vigilante cuts a violent swathe through the Yakuza, corrupt politicians, and international syndicates, his journey evolves beyond simple revenge. He adopts the moniker "Hit-Monkey," becoming a legendary, terrifying urban myth. Bryce serves as both a tactical advisor and a sarcastic moral compass, though their dynamic is fraught with bickering over murder ethics and past regrets. Concurrently, an idealistic, disgraced police officer named Haruka, alongside an ambitious politician named Akiko, navigates the city's treacherous power structures. Haruka becomes obsessed with capturing the mysterious monkey assassin, believing he is the key to cleaning up Tokyo’s deeply entrenched corruption, unaware of the vast conspiracies pulling the strings behind the scenes.The narrative escalates when Hit-Monkey crosses paths with Lady Bullseye and other elite killers, realizing his rampage is merely a symptom of a much larger war for the soul of the city’s underworld. Akiko’s storyline intertwines deeply with the mob after her uncle, a powerful crime boss, is assassinated, forcing her to embrace her own dark ambitions to survive and consolidate power.In the explosive climax, Hit-Monkey confronts the masterminds orchestrating the chaos, culminating in brutal, high-octane showdowns that test his limits and force him to choose what kind of legacy he wants to leave. Having decimated the hierarchy of Tokyo’s criminal elite, Hit-Monkey ultimately finds a strange, reluctant peace. With Bryce’s ghost finally finding some measure of redemption and fading away, the monkey transitions from a mindless instrument of slaughter into a true protector of the helpless, establishing himself as a permanent, feared fixture of Tokyo's shadowy criminal landscape.