Kouko is Fuuko's older sister. She used to be an art teacher at Tomoya's school and she treats everyone kindly. Kouko is one of the familiar faces in the Furukawa Bakery, and Nagisa admires her very much, being her former art teacher. Currently, she is engaged to Yusuke Yoshino.

In the movie, Kouko was a drama teacher instead of an art teacher. She, along with Youhei and Tomoya, helped supervise and revive the drama club for Nagisa.