Driven by an intense curiosity about male anatomy, Kasuga enters into an academic bet with her classmate, Kobayashi. After both achieve perfect scores, their agreement leads to a series of bold sexual explorations as the two students experiment with each other's bodies and discover the pleasures of intimacy for the first time.
After discovering books on human anatomy and discussing the nature of sex, Kasuga and Kobayashi decide to explore their physical desires while walking home in the rain. What begins as an attempt to simply "make each other feel good" quickly escalates, leading the pair to prioritize firsthand experience over their studies as they succumb to their mutual attraction.
Kobayashi and Kasuga, childhood friends who have grown distant, are assigned to clean the gym storeroom together. Amidst the stifling heat and an unexpected emergency, the tension between them breaks, leading to a mutual confession of their long-held feelings. Their reunion culminates in a passionate intimate encounter, sealing their decision to rekindle their relationship and start dating.
Kobayashi and Kasuga set out on their first date with plans to visit a planetarium, but their priorities shift when they decide to visit a drugstore for condoms first. Overwhelmed by their excitement, they skip the romantic outing and head back to Kobayashi's place. After some clumsy attempts at using protection, the pair shares an intimate encounter, discovering the sensations of their first protected experience together.