She is a third year student and the Calligraphy Club's President. On the outside, she is a mature upperclassman, with a playful attitude and a kind spirit. She enjoys calligraphy and tends to make a huge mess whenever she is writing. She always seems to be at odds with Yuika and teases/picks on her, the same goes both ways.

Spoiler

However deep down Sayuki is actually a huge masochistic pervert. She has a fetish for being dominated and wants Keiki (whom she likely holds feelings towards) to make her his pet. She proclaimed that she was envious of a dog and owner whom she interacted with as she wants to have that master-servant/owner pet relationship with Keiki.

(Source: Kawaikereba Wiki)