Shouji Osamu is an elementary school teacher fresh out of college about to embark on his first day. At the school gate, he was suddenly hugged by Chise, a girl he doesn't recognize who seems to know him. He later finds out that Chise is a fifth-grade student in his class, and that she lives in the same apartment building as he does. During a late-night rendezvous, he learns that nothing about their encounter is coincidental.

Note: Chapter count includes one bonus chapter.