I'll redo that day to change your fate. This is a painful love story about a relationship gone stale between a tough yet gentle gym trainer and an awkward, romantic high school teacher .

If I could redo that day... Natsu, a math teacher, has been dating Yuu, a gym trainer, for ten years, and they've lived together for five. Natsu always feels how physically compatible they are when they have sex, but something feels like it's missing now that their everyday lives have lost the excitement of their early relationship. One day, Natsu slips at school and hits his head, losing consciousness. When he wakes up, he's gone ten years back in time! He reunites with Yuu in a nostalgic town wearing a school uniform and it makes him remember those exciting days...