Amagami SS: Little Sister

Miya Tachibana, assuming her annoying brother Junichi will be unlucky in love and alone forever, decides to spy on him at school after hearing that some of her friends find him to be kind and caring. Through her spying, she learns that he gets along well with girls at school, which results in an even bigger misunderstanding, as Miya wrongfully assumes he likes men since he doesn't have a girlfriend. However, after she herself rejects a boy, Miya starts questioning how she views Junichi as she is reminded of Junichi's similar experience from two years earlier.

(Source: MAL)