Yassan

Yaasan, otherwise known as Literary Girl, is a character in Daily Lives of High School Boys

Background
Literary girl first makes her appearance in High School Boys and Literature Girl where she pesters Hidenori at the river bank. She seems to always go there, knowing Hidenori reads there, to have what he calls "a boy-meets-girl scenario near a river bank". Also, we may not know for sure, but it appears that Yas-san has taken interest in Hidenori, due to the fact that when he caught her walking with a classmate, she chased him all around town to the bridge just to tell him that it was, so he wouldn't get the wrong idea.