Takashi and his wife, Kanon, have been married for two years. Wanting a child, they engaged in 'pregnancy preparation' by having Takashi abstain from sex for a month to produce healthy sperm during the fertile window before ovulation. On the other hand, Kanon's sister Megumi, who works as a flight attendant and travels frequently, struggles to conceive with her husband. Eager to have a child before her younger sister, Megumi visits Takashi on his planned conception day and seduces him, taking all of his accumulated sperm.
