After narrowly avoiding a terrible fate at the school festival, Kou renews his friendship with his old classmates from Research, Asagiri and Isumi. As they pass the time peacefully, Asagiri decides to confess her love to Kou. However, the very next day, Isumi informs Kou of some shocking news—Asagiri has disappeared in the kihei-infested ruins! As he searches for her, a new threat appears which may shed light on the true nature of the kihei. For the sake of his beloved Brides, Kou must make a choice.