One day, you arrive at Kurenai Academy in Shinjuku. You're a completely ordinary student, and one of your new classmates gazes at you - Masamune Shiga.

The class president, Sayuri Mifune, gives you a tour of the school, during which you spot what appears to be a ghost wearing a summer dress. You investigate the area, when you suddenly encounter an evil spirit that's been haunting the academy.

The ghost is wearing a red coat, and he quickly attacks! You're rescued by your classmate, Masamune, and a mysterious woman...

You team up with Masamune and the woman to exorcise the murderous red-coated spirit. After the battle, the woman tells you exactly who she is. She explains that she runs a company which takes on requests from citizens to exterminate ghosts like this one. Her name is Chizuru Fukurai, and she invites you to join her company - Gate Keepers. You decide to accept her offer.

And this is how your new life as a member of Gate Keepers begins. It also signals the beginning of the life-or-death battle against the evil spirits lurking within the darkness of Tokyo...

[From official site]