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.

Kusakabe Tsubomi is a cheerful, sporty 10-year old girl - but lately, she's been nothing but angry, and it's all because of a certain alien called Clow Zet from the planet Bal Coni, who's come to observe how the boys and girls of earth live. From first periods to underarm hair to all the insecurities and concerns about sexuality that came with becoming an adult, it's all tied together within the love story that is the second volume of the immensely popular Naisho no Tsubomi! A complete, stand-along story that's different from first!