My aunt and father remarried... ~And Aunt Michiru became my mother~

Fumio's aunt, Michiru, was kind and caring for Fumio, who was desperate after losing his mother. One summer afternoon, Michiru and Fumio end up having a forbidden relationship that only happens once. Several years later, when the memories of that summer are still fresh, he hears that his father and Michiru are getting married again... Fumio can't hide her joy at living with Michiru, who has become a new mother, but every time she imagines Michiru being held by her father, an unpleasant thought takes over her head...