How far can we fly before we have to come down? Little by little, everyone in their first year of junior high school has begun their transition into adulthood. However, Akane Mizutani finds it difficult acting mature. On an off chance, she meets Tooru Tsukino, a boy in her class with mysterious rumors surrounding him—rumors that make even Mizutani think of him as strange.

With their encounter, Mizutani finds out the truth of Tsukino and the similarly odd girl Hiki. With Mizutani and Tsukino forming a promise at the schoolyard regarding each Monday night, the story depicts the relationship and encounters with each other, the alienating idea of growing up, and the truth of one's character.