Ayumi Umino has always looked up to people like Mizuki Otonashi; even with a terminally ill mother, Mizuki has managed to top their class in both popularity and kindness, to the point of not revealing that Ayumi cut class to drink alcohol. One day, Ayumi is approached by Mizuki's friends and asked to return Mizuki's painting set to her—despite her dark attitude toward the shallow girls, Ayumi accepts as a way to repay Mizuki's kindness.

However, as Ayumi arrives at Mizuki's house after taking a shortcut, she sees something she was never supposed to—Mizuki stepping out of a car, covered in blood and carrying a knife. Ayumi feels death creep near as Mizuki approaches her, but is surprised when she is instead invited inside for tea. She nervously accepts, now a witness to murder and scared for her life, but is curious about this side of Mizuki normally hidden from the public.