Yuuki Umemiya

Yuki is Saji's busty childhood friend and somewhat an unintentional rival to Koizumi. Yuki has grown well-proportioned and shapely. However, her charm and body, while still able to make guys drool, are not as effective as Koizumi's grace and mystery. Due to that fact Yuki has low self-esteem.

(Source: Wikipedia, edited)