Hayato Ibuki, a journalist for an occult magazine, is investigating mysterious suicides that have been happening at Shinjuku Station. While he's investigating, a black shadow pushes him onto the tracks. At the last moment, a beautiful girl named Balucia saves him and hands him a case. The case, like Pandora's box, should not be opened.
Inside the case, you find the demon gun Gangour, a tool used to capture and use demons and fallen angels. Hayato uses it to turn a demon into a team member. With the Gangour in hand, Hayato, accompanied by the self proclaimed angel, Lua, investigate mysteries around the country while looking for that beautiful girl. Little does he realize that he is caught between the ambitions of the dark rulers and the expectations of the angels...
Hayato is given a case by the mysterious, beautiful girl, Balucia. One day, an angel named Lua appears before him, claiming that he is the Chosen One. While Hayato is walking around the Shinjuku area with Lua, he is attacked by a hooded figure who it turns out is a demon called a "Deep One." Hayato powers up the Gangour, captures, and then uses the demon. Lua, while supporting Hayato, tries to look for her missing sister, Balucia. Hayato and Lua head to Akihabara to investigate a mysterious rumor.
An evil demon stands behind Balucia, who has gone missing...
Why did Balucia disappear? Where is she right now? Hayato and Lua search for the truth.
Balucia, who now seems completely different, approaches Lua and Hayato.
What happened to her...?