Twenty one year old Makoto Majima lives in the Ikebukuro district of Tokyo, an area notorious for juvenile crime and gang activity. He is known locally as a troubleshooter, a cool headed young man with a talent for diffusing tense situations and solving problems that the police cannot or will not handle. While not a formal member, Makoto is closely associated with the G-Boys, the most powerful youth gang in the area, whose leader is his old high school friend, the charismatic and athletic Takashi Andou, known as the King of Ikebukuro.

The story begins when Makoto is drawn into a brutal and personal case: the murder of his close friend Rika. As he navigates the dangerous and crowded streets to find her killer, he becomes more deeply entangled in the underworld he usually tries to keep at arms length. Following her funeral, Makoto learns that Rika was secretly dating men for money, and a suspicious figure appears at the service, deepening the mystery.

This initial tragedy sets the stage for Makotos role as the go to mediator for a wide range of clients, from desperate parents to yakuza bosses. In one case, he is forced to find a crime lords missing daughter to avoid losing a finger. In another, he helps a friends boyfriend who is being hunted by the yakuza after angering a powerful drug dealer. His reputation for solving problems leads to requests to catch a stalker harassing a woman on a voyeuristic website, to investigate a cult-like pyramid scheme his own mother has joined, and to negotiate the safe return of a kidnapped child prodigy.

The series is structured around these episodic cases, but a significant narrative arc involves the escalating turf war between the G-Boys and a rival gang, the Black Angels. The conflict intensifies drastically after a man in yellow stabs a girl named Kana, and suspicion falls on the G-Boys. As tensions boil over, the Black Angels openly declare war on the G-Boys territory. The violence takes a tragic turn when Makotos close friend Shun is killed in the crossfire. Consumed by grief and rage, Takashi abandons his usual restraint and adopts increasingly drastic and violent measures to crush their enemies, threatening to tear the community apart. Throughout these events, Makoto must use all his wit and influence to protect his friends and restore a fragile peace to the streets of Ikebukuro.