Parasol Doumei

A boy who is a twin lags behind his overachieving brother in both academics and popularity. He proposes to the girl he likes, herself a twin, but had confused her for her twin sister. Embarrassed and in a compromising position, he agrees to help her to win the affections of the boy she likes, his brother, lest she leaks his botched confession to her sister, hampering his chances with his crush.

(Source: MU)