Tachibana Tsubomi is an 11 years old 5th year who is a little on the shy side. Soon after becoming friends with Saya after discussing her mother's pregnancy, Tsubomi faces her first period, her friend Yae purchases a bra, and Rea begins to grow hair in new places. Little by little their bodies are maturing, boy and girls have problems they can't discuss, just what is the body of an adult like? This widely-acclaimed serial builds heart-pounding romances and painful friendships revolving around Tsubomi's concern about sexuality.