Haha, how cute. They're playing around because they like each other. If Hiyori really hates someone she is cold and quiet. Slapstick is her love language. I get the impression Hitsugaya finds her cute; especially since she is a childlike adult just like him.
this randomly popped up in my feed and im glad it did, Bleach characters had so much character i still adore it after 10 or more years and that says quality, condolences to Tite as well