Yassan is a highschool girl from Sanada West High who has long dark violet hair reaching on her waist. She makes her first 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, it appears that Yassan has taken an interest to Hidenori, due to the fact that when Hidenori caught her walking with a classmate, she chased him all around town to the bridge just to tell him what their relationship was, being just friends, so he wouldn't get the wrong idea. In the manga, she is very interested in Hidenori.
At the end of the anime, they seem to get together, quoting lines to do with the wind, then Hidenori after saying "Let us make haste, lest the wind ceases" reaches his hand out for Yassan and Yassan then takes Hidenori's hand.