Ikai Tettai Parabellum

On his way home, well-adjusted high schooler Koma Higurashi dozes off on the train and awakens at a station he’s never seen before. Moments later, Mayuru—a girl who has gone missing—rushes into Sasagi Station, and an unexpected shootout erupts. In the chaos, Koma comes to understand that he has stumbled into a mysterious alternate realm.