Koichi Kawai (Arata Horii), an instructor at a gymnastics school for children, is found dead in the classroom. The night before, someone supposedly knocked him over and hit him on the back of the head with an iron bar. Satoshi Itomura (Takaya Kamikawa), who was there, found a pencil that prayed for passing the exam among Kawai's belongings. The pencil has a scratch that looks like it was gouged where he puts his finger, and Itomura wonders why there is a scratch in that place.
As Itomura begins his investigation, he meets Marika Tomiike (Saai Koyama), a second-year elementary school girl who visits Kawai's room. She says that Marika learned gymnastics from Kawai when she was in kindergarten, and even though she left the classroom, she still admires him, and she exchanges 'exchange notes.' Marika also reveals that her mother, Kotone (Aki Maeda), is dating Kawai. Kotone was a single mother who raised Marika on her own while working as the proprietress of her parents' kimono store.
However, when she asked Kotone about her situation, she confessed that she broke up with Kawai about a month ago. She just can't tell Marika about it, and she testifies that she hasn't seen him recently. However, just then, it is discovered that Kawai was heavily involved in Kotone's family's past! 'The investigation takes a sudden turn...!?'