This is the Masked Ballroom: a place where people revert to beasts, let go of reason, and revel in freedom and anonymity. Here, with the help of a "monster supplement," anyone can transform into beasts and do as they please. It's the only "government-approved slum," where people can forget the suffocating atmosphere of the surveillance state. It's in this city where Reiji, a young vampire and a real monster, alongside his werewolf partner Tsuki, take on the task of keeping the streets clean. They search for centaurs who have committed hit-and-runs and fight life-and-death battles against the urban legends that manifest. And a meeting with the "Medicine Witch" will change the fate of Reiji and his friends...