Some time ago, the influential and powerful Toue Inc. bought the island of Midorijima, Japan, with the plans of building Platinum Jail—a luxurious utopian facility. Those who are lucky enough to call it home are the wealthiest citizens in the world. The original residents of the island, however, were forced to relocate to the Old Residential District; and after the completion of Platinum Jail, they were completely abandoned. Rib and Rhyme are the most common games played on the island. Rib is an old school game in which gangs engage in turf wars against each other, while Rhyme is a technologically advanced game wherein participants fight in a virtual reality. To be able to play Rhyme, you must have an All-Mate (an AI that typically looks like a pet), and the match must be mediated by an Usui. Aoba Seragaki has no interest in playing either game; he prefers to live a peaceful life with his grandmother and All-Mate, Ren. However, after getting forcefully dragged into a dangerous Rhyme match and hearing rumors about disappearing Rib players, all of Aoba's hopes of living a normal life are completely abolished.

Rem is an ordinary woman in our world but, in the world of dreams, she becomes a dream warrior, defending humanity from the evils there. When dream demons reach the waking world, she fights them with the help of her pets which transform into a tiger and wolf.

The word cerebrum refers to a gigantic system consisting of collision universes, which is called cerebrum universe. The story starts from a series of unknown murders, unravelling the secret hiding beneath the entire universe, ranging from horrifying conspiracies to galaxy wars, from anti-human betrayals to honourable sacrifices. Having realised her weakness and backwardness, mankind takes the last stand. (Source: Official website)

Although peace has finally returned to Ikebukuro, many of the odd occurrences have become common sights around the city. One such case is the police's constant pursuit of Celty Sturluson, the Headless Rider. Moreover, someone has placed a large bounty on her, igniting the motivation of gang members all over to begin searching for the supernatural creature as well. Meanwhile, Mikado Ryuugamine is approached by Aoba Kuronuma, a mysterious underclassman with unknown intentions, who reveals that he knows Mikado's true identity. But Ikebukuro's state of tranquility is short-lived, as a new threat appears in the form of a murderer who goes by the pseudonym Hollywood, known for wearing a different mask each time they commit a crime. As the various events taking place prove to be connected yet again, Ikebukuro is thrown into another conflict that threatens to engulf the entire city in chaos.