立花 耶也子

Yayako is a new student at Seio who becomes a treasurer of the student council. Sakura, her senpai, calls her "Yaya-pyon" (she hates this name), and she calls her "Tsuchii" in return.
She had entered the student council by Sakura's recommendation. 

Taken from url=http://en.wikipedia.org/wiki/List_of_Otome_wa_Boku_ni_Koishiteru_characters#Otome_wa_Boku_ni_Koishiteru:_Futari_no_Elder.