Naisho no Tsubomi v01 tells the story of Tsubomi Tachibana, a fifth grader dealing with issues such as her mother's pregnancy, her first period, and the strange feelings she has started to get when she has been around boys.

Naisho no Tsubomi v02 tells the story of Tsubomi Kusakabe, a fifth grader, who encounters an alien wanting to do research of earth. It turns out he has picked Tsubomi to be his research subject.