烏橘 沙世子

Sayoko, is same grade as Hatsune, is Kanako Ukitsu's younger sister, but she is crisp. She is a treasurer of the student council in the second grade and is the vice-president in the third grade.

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