Will_0_Wisp
Phin has her life sorted out already, and it doesn't include other people in it.
She didn't want to spend her precious free time looking after a bunch of bratty little kids, even with her cute coworker dealing with most of the tantrums. She didn't want to be thrown into art club, and an art competition that's basically a popularity contest! And she DEFINITELY didn't want to hand over one of her precious button pins to said coworker, who doesn't even know her name.
But it makes her feel... happy? when he wears that pin on his backpack, like he's showing it off.
Okay, so maybe her life plan has room for at least one more person.