After losing his mother, Fumio fell into despair, but his kind and caring aunt Michiru quietly supported him. One summer afternoon, Fumio and Michiru crossed the line into a forbidden relationship—just once. That memory never faded, deeply etched into Fumio's heart. Years later, his father married Michiru, making her his new mother. Fumio found joy in this new family life, yet whenever he pictured his father making love to Michiru, dark desires stirred within him. Living under the same roof, Fumio struggles with the conflict between his past memories and his growing, forbidden emotions, unsure of how to face his own feelings.