Sakagami Mamoru is a university student who is living alone because his parents traveled abroad for work. His neighbor, Tamura Chihaya is a meek and timid housewife with a young daughter.

Since the husband is always busy with work and comes home late, Mamoru, despite going to classes and working part-time job everyday, looks after Chihaya's daughter when she goes to work due to her family's dire financial situation.

Mamoru is secretly in love with Chihaya and thought he would never convey this feeling to her. However, one incident leads them to commit a mistake which will change their relationship forever.