Sakuradaimon is the school's prefect. A prefect is a student who is authorized to enforce discipline. As a prefect, he's supposed to be a role model to other students, but unfortunately he's not perfect. Kohinata is one of the people who Sakuradaimon has tried to discipline into wearing appropriate school attire, but she has thusfar been disobedient.
And so this is a story of the two interacting with one another.