A story depicts a clandestine sexual relationship between a young man named Naoki (also called Nao) and a married woman, Mizuho, who is the mother of his friend, Nami. Under the guise of a study session, their encounters quickly become intimate, progressing from kissing to oral sex and eventually full intercourse, often while risking discovery by Nami or Mizuho’s husband. Mizuho actively encourages Naoki, comparing him favorably to her husband and becoming increasingly infatuated with him. The entire affair is a secret they must keep from the rest of the family, leading to several tense and close calls.