Rei, a high school girl, becomes trapped in Purgatory where the souls of the dead are tormented. After awakening with incredible powers, Rei accidently kills her dearly loved little sister, Mirai, whose soul may be lost forever. To bestow Revival upon her sister, Rei makes a contract with the Demons of Purgatory and agrees to fight monsters for them as their Executor. Rei battles through the many levels of Purga tory, making friends and foes along the way. As she fights, evil continues to assail and torment her. It's only by confronting her own feelings and mistakes--and expressing them through tears--can Rei overcome the true evil lurking in Purgatory.