In a near-future Japan where all government functions have been fully privatized, law enforcement has become a competitive business. Countless Private Security Police, or PSP, now investigate crimes based on profit and loss, leaving the vulnerable behind. In the heart of Tokyo, the red-light district of Shinjuku's Kabukicho has become a haven for society's weakest, a place where crime runs rampant and is often ignored by profit-driven corporate police. It is here that the Iwai Private Security Police, a tiny, impoverished office run by a lazy but principled man named Shunsaku Iwai, operates from the second floor of a rundown gay bar. Despite being perpetually broke, Iwai takes on the cases no one else will, from murder and fraud to searching for lost items and missing persons, driven by a deep-seated hatred for crime inherited from his father, a former police officer once known as the Guardian of Shinjuku who was killed in the line of duty.

Shunsaku Iwai may be a slacker who spends his days watching online videos, but his sole source of pride is the bond he maintains with the local community, a legacy from his father. His only employee is his complete opposite: Hannibal Lee, a cold and handsome man with a sadistic tongue and a mysterious past as a wanted international terrorist. Ironically, Hannibal despises animals. To assist in their investigations, they rely on Dandy, a multi-functional AI unit known as an Animal Unit. However, Dandy was state-of-the-art a decade ago and is now essentially a broken-down, obsolete piece of junk. This mismatched team of a lazy chief, a former terrorist, and an outdated robot police dog forms the backbone of the IPSP, struggling to make ends meet in a cutthroat world where profit is the only law.

The narrative kicks into high gear with the opening arc, The Boy and the Dog. When a man is found dead in a back alley of Kabukicho, a young boy arrives at the IPSP office, seeking help. This seemingly small case quickly escalates, drawing the team into a violent conflict with Silver Rhinoceros, an elite private police force, and a full-blown gang war with the local mafia. The following arc delves into the history of this privatized world, focusing on the Rampage of the Metropolitan Police Department Era. The investigation forces the team to confront a dangerous legacy left behind by the old police system, as Hannibal's hidden memories begin to surface. As the case unfolds, the narrative explores the connection between Hannibal's past, Shunsaku's mission, and a truth referred to as the Dogs Memory, leading to a deeper conspiracy that only this tribe of misfits in Kabukicho can unravel.