Youko is Shinobu's classmate and has been friends with Aya since middle school. She loves giving Aya a hard time—like the time she told everyone that Aya was basically glued to her side back then because she was too nervous to go anywhere alone. Aya obviously denies this.
On the surface, Youko's all energy and athleticism, the type who's always fired up about everything. But she's actually one of the more grounded people in the group, along with Aya and Alice. She's got a few younger siblings she hangs out with and plays around with a lot. Aya's noticed that Youko's little brother sounds almost exactly like her, which is kind of funny.
Content compiled by AnimeList.moe from publicly available sources.