Everyone in their First Year of Junior High School little by little are becoming adults. However, Akane Mizutani still finds difficulties in changing into a grownup. One day, she meets Tsukino Tooru, who has strange, mysterious rumors surrounding him for someone appearing harmless.

With their encounter, Mizutani finds out the truth of Tsukino and another odd girl, Hiki. With Mizutani and Tsukino forming a promise to meet at the schoolyard every Monday night, the story depicts the relationship and encounters with each and one another.