Karneval Nai searches for someone important to him, with only an abandoned bracelet as a clue. Gareki steals and pick-pockets to get by from day to day. The two meet in a strange mansion where they are set-up, and soon become wanted criminals by military security operatives. When Nai and Gareki find themselves desperate in a hopeless predicament, they encounter none other than the country's most powerful defense organization, "Circus". The Circus is a Defense organization that works for the government. They perform raids to capture criminals and solve crimes that the Security force otherwise cannot handle. After their raids, they put on shows as an apology for scaring the citizens. Their group consists of the strongest, most capable fighters that use a special type of bracelet, known as Circus I.D., to fight.