Sayo is a classmate of Rin's and shows up as her most devoted fan from early on. The two go way back—they've been childhood friends since kindergarten and stuck together through elementary school and partway into middle school.
She first appeared in episode two. Later, in episode 8, you can spot her in the crowd during an Earphones performance, and she shows up again in episode 10. The long history between them clearly matters; fans often note how their bond feels genuinely rooted in shared history rather than just casual school friendship.
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