Yokohama's Suribachi district is a lawless zone swarming with all kinds of people. To protect each other, a group of teenagers created a self-defense organization called Sheep, with 15-year-old Chuuya Nakahara as their "King." Thanks to Chuuya's powerful ability to control gravity, few dare oppose the Sheep.

However, worrying news spread around Suribachi: the Port Mafia's deceased leader has been witnessed roaming around. His successor, Ougai Mori, sends his protege Osamu Dazai to uncover the truth. While investigating, Dazai runs into Chuuya, and a fight erupts between the two. But before Chuuya can deal the final blow, the Port Mafia captures him.

Mori offers Chuuya a deal: if the teenager helps unravel the mystery behind his predecessor's alleged resurrection, the Port Mafia will not harm any of Sheep's members. Backed into a corner, Chuuya reluctantly accepts. As he and Dazai are paired together, they must overcome their disdain for each other to save Yokohama. Unfortunately, the appearance of Arahabaki, the "God of Calamity," threatens to hinder their plans.