Hiromi, a timid and quiet protagonist, was raised strictly by her grandmother. Due to her grandmother's abuse, Hiromi created an imaginary version of herself in the mirror, named "Yumi," and would play by talking to her as a child. By the time Hiromi becomes a high school student, she only remembers playing with the mirror, but one day, she hears a voice from the mirror asking, "Is what Grandma says really right?"

Triggered by this voice, Hiromi's alternate personality, "Yumi," who can freely control Hiromi's body, begins to venture out into the night without Hiromi's knowledge... This is a suspenseful story about Hiromi confronting her true desires and her complicated relationship with her grandmother.