The rumors about Ikebukuro spread quickly, particularly concerning the brutal battles for territory between rival color gangs and the infamous legend of the Black Rider. Due to his parents' professional commitments, Miyoshi Yoshimune is forced to attend Raira Academy, where he befriends Mikado Ryuugamine, Masaomi Kida, and Anri Sonohara. They warn him to stay away from gang activity and ignore the baseless myths in order to protect himself.
Unfortunately, danger lurks for those who encounter Izaya Orihara, a notorious information broker from Shinjuku. Even though Yoshimune's friends assure him that Izaya is joking, a chance encounter with the broker leads to him being assigned a mission: investigate the anonymous people who are attempting to infiltrate the color gangs, and report back to Izaya. Reluctantly, Yoshimune agrees to delve deeper into Ikebukuro's criminal underworld at Izaya's request, leading him to a critical meeting with a young woman named Chiaki Igarashi. This meeting is just the beginning of Yoshimune's journey into the most significant plot to hit Ikebukuro yet.