A girl named Rei and Mirai, her little sister, are dragged into the afterworld of Purgatory by an unknown entity. Scared and confused, Rei tries to lead them home when they are attacked by a terrible monster.To protect her little sister, Rei unlocks the strength hidden within her. With it, she fights against the dead Souls of Purgatory.

However, this power turns against her. Rei accidently kills Mirai with her very own hands, thinking she is an enemy.

Devastated, Rei weeps hopelessly at what she has done. Sensing an opportunity, two Demons appear and whisper in her ear...