The Masquerade-where people can throw off the shackles of society, revert to animalistic behavior, and revel in freedom and anonymity. In this government-designated slum, the pharmaceutical company Beast Tech distributes Monster Tonic, which transforms humans into Beastpeople. In a place so rife with violence and immorality, the cleaners from Fantastic Sweeper must clean up the mess...and any bodies. The vampire boy Reiji, the werewolf Getsu, and the new addition to their team, Kei work as cleaners. On behalf of their classmate Mei, they are tracking down the unstable Mythic Tonic which leaked from Beast Tech and resulted in the death of her friend. In the process, an unprecedented tragedy unfolds. And after the dust settles, the reported death count includes...three high school students.