Koyoshi

is a high school student who attends Saint Ishiyama Academy where she has participated in the school's special event, Saint Saint X'mas, with a fellow high school student named Yamaka.

Saint Saint X'mas Arc
Koyoshi and Yamaka participate in the Saint Saint X'mas competition together where they advance to the Top 16. In the first round, they are selected to go twelfth, pairing off against the Nishizawa-Yonehara pairing; ultimately, they end up losing in the first round.

Yamaka
Koyoshi and Yamaka participated together in a Saint Saint X'mas competition on Christmas Eve.

Etymology

 * The surname Koyoshi means "sun, day" (日) (ko) and "lucky, good" (吉) (yoshi).