Setsu

A small-animal type.

Setsu grew up with Satoru ever since they were small children, and they were always close.  It was not uncommon for Satoru to show up at their door in the middle of the night and ask to stay over; Setsu's mother was always understanding about it, and around grade 4 they were constantly sleeping together.  Satoru would hold hands with Setsu until he fell asleep. At age 12, they discover a fawn that has apparently lost its mother somehow and bring it home; with Setsu's mom's permission, they kept him and named him Jutta, and raised him together like their own child.  Around their second year of middle school, Satoru started distancing himself from Setsu and Jutta, which nearly broke her heart even as she tried to hold on to him.

In their first year of high school, in spring semester, Setsu was asked out by a boy in another class; she tried going out with him, but when he tried to kiss her despite protest Satoru slugged him.  The relationship ended there.  Later that year, in fall semester, Setsu was hit by a car while trying to save Jutta, and her relationship with Satoru improves afterward.

They eventually marry, and Setsu becomes a piano teacher.