In a quiet corner of a bustling high school, a shy but determined student named Hina-chan finds herself in a delicate yet passionate relationship with her boyfriend, who is also a fellow examinee striving for the same university. Their bond deepens with every study session, every shared dream, and every quiet moment of affection. But as exam season approaches, Hina-chan is faced with a dilemma — a promise to her boyfriend’s birthday, and a sudden lack of allowance. Desperate to celebrate, she turns to a new venture: a part-time job known as "papa-katsu," where she exchanges a bit of saliva for a generous sum of money.
At first, it seems like a harmless way to earn some extra cash — a small price to pay for a special birthday. But as the situation unfolds, the teacher, who has long been a quiet observer of Hina-chan’s life, steps in, revealing the truth. The teacher, who once had a similar relationship with her own students, is not ready to let Hina-chan’s secret — and her boyfriend’s dreams — slip away without a fight.
What begins as a simple exchange quickly turns into a playful yet intense challenge, where the teacher pushes Hina-chan to prove her sincerity, not just with words, but with action. The stakes are high — if she fails, it might cost her the chance to be with her boyfriend in the same university. As the classroom becomes a battleground, Hina-chan’s determination is tested in every way, from physical endurance to emotional strength.
Through every trial, every challenge, and every moment of embarrassment, the bond between Hina-chan and her boyfriend only grows stronger. As the teacher’s playful yet strict methods continue, the two students must prove that their love — and their future — is worth every sacrifice. In the end, as the final promise is fulfilled, it becomes clear that their journey has only just begun.
