Oujisama nante Iranai

Kotoko is a very ordinary high school girl who exercises, studies, and looks normal. The only thing that isn't typical is that she has a childhood-friend fiancé! Moreover, her partner, Isho Nishizono, is the best handsome prince in school! Kotoko is in a situation many envy, but for some reason, she's desperately hiding the engagement.

This is the opening of a doki-doki school romance about an ordinary girl and the school prince.

(Source: Ohzora Shuppan, translated)