Kazumi thought he was good friend with a boy he had known for ten years, Rihito. One day, while they were out in town together, looking for a shop selling masks for their school's masquerade ball, Rihito suddenly disappears. Kazumi drops school and starts looking for him, and will soon set foot in a totally new world. In an abandonned factory thought to be haunted, he ends up face to face with a group of demons. Running away, he finally finds Rihito, one week after he disappeared. His friend seems to go well but his personnality changed. Rihito seems to be able to lead them and is surprised that Kazumi can see the demons. He announces to Kazumi that he always hated him. Distressed, Kazumi doesn't have time to react for the demons attack him again. A mysterious creature then appear out of his body and get rid of the monsters.
From now on, Kazumi is going to discover a new side of the city he lives in. A city in which demons et personae live (fighting creatures that people with the same powers as him can invoke) Kazumi will be guided in this new world by the three people who live hidden in the factory, and also own Personae.