This story is about "Puellarium", a school isolated from the outside world by fog and thorns. Here strict discipline is always in effect, where the air is always tense and time is never disturbed. However, one morning a girl was found unconscious in front of the school gate. This gate is always closed and should only open on special occasions. The guards, on alert, asked her to name herself to which she replied "Alouette."

At that moment, the bell of the clock tower, which was rusty and always silent, rang out. "When the bell of the clock tower rings, the end of this school will come soon." Like the gossip had hinted, it was the beginning of a nightmarish turmoil in Puellarium. Alouette who had become a student after many complications violated curfew and left her room. What she saw there was a school that had turned into a different world, and a strange shape that wandered around with murderous intent. With determination, she called out to the girl in front.