Yuu Matsumi
Yuu is a third-year student at Achiga Girls' Academy in Nara Prefecture and one of the main characters in the "Saki Achiga-hen episode of side-A" spin-off manga. She's Kuro Matsumi's older sister.
Probably her most distinctive trait is how sensitive she is to cold—she bundles up completely no matter the season, even when everyone else is in summer clothes. It's become pretty iconic to her character.
When she was younger, Yuu actually wanted to join the school's mahjong club but held back because she worried it would feel weird joining as an older student. That hesitation eventually changed, making her part of the club's core group.
Content compiled by AnimeList.moe from publicly available sources.
