Yuki Kira's traumatizing past causes her make a contract with a demon and gain immense supernatural powers from a fragment of the Akuma Crystal - a mineral from a meteorite that fell to Japan thousands of years ago. Only young girls who are compatible with it can gain these powers. Other will become possessed by the demon inside the Crystal and they will be overcome with negative emotions and commit crimes. After gaining her powers, Yuki joins the Secret Murder of Sinners Organziation (SMSO) to kill those who have committed vicious crimes. However, after discovering what the SMSO really does 6 years later, she quits the SMSO and vows to destroy them. However, she has a lot on her shoulders: putting criminals to rest of her own accord, a 250,000,000 Yen on her head, and dealing with the SMSO.