Tsuyoshi has decided to live with his father's new wife, Yuna. However, Tsuyoshi begins to notice something strange about Yuna. Yuna is always without a bra at home... Naturally, Tsuyoshi, who has reached the age of puberty, gets aroused when he sees a glimpse of Yuna's nipples, who is a stranger to him even though she is a family member. And Yuna, who is actually not satisfied with her husband's dick, gently seduces Tsuyoshi...