Ririko lost her parents and siblings in a mysterious incident where details remain in the shadows. Before Ririko moves to her new home in Kaminoshiro, a detective gives her a letter that her father wrote before his death, which contained a card with a black and white checkered pattern on it.

At her new school, Ririko becomes friends with Maya and has some interest in a male student named Shirou. She questions about the black clock tower that stands in the center of the town, but no one bothers to answer the question. Her new life in her new home seemed all as well until one day Maya calls Ririko out and takes out the same checkered card that Ririko was given to her and she summons some unknown creature! As Ririko is in confusion as to what's going on, Shirou appears and says "Not another one..." What's going on around here?