Matsuzaka is a former softball pitcher from a team of which Haruna played against in middle school. She arrived to Haruna's school due to her father's sudden transfer. She gives off a charm that she uses against boys to do what she wants (such as trying to get a male students seat number in order to sit next to Haruna).

Spoiler

She has given off intense glares to Haruna who thought it was staring from admiration. Haruna soon learns of her identity but Mami knew of her from the start assuming Haruna had already knew.