#bunny's usage of 'elsie' would be more to mess with her more tongue-in-cheek as described here

[therentyoupay]

Reading two homes (aaaahhh love it so much thank you for writing it) and just gotta say I am loving the Bunny and Elsa bromance.

THANK YOU SO MUCH FOR YOUR ASK AND YES, YES, THANK YOU FOR ALSO SHARING IN THE JOY OF A BUNNY/ELSA!BROTP.

while writing at the center, their brotp shenanigans became some of my favorites. 😭 i also had a lot of fun exploring potential nuances of elsa's would-be friendships with each of the guardians in cosset, which is where i became obsessed with the idea of which nicknames they would (or would not call) elsa, and what each nickname demonstrated about their friendship (e.g., bunny's use of "ice-pop").

there's a whole thing about what each of the guardians call her, but here's the bit from cosset about the bunny/elsa!brotp and how "ice-pop" came into being (and is now a permanent fixture in my head and transcends multiple stories, lmao):

Bunny calls her the Snow Lass at first. It is uncomfortable for him, being around a human (and then a newborn Guardian) who has always struggled so deeply with Hope. Then one night, sometime around her eleventh year, the two of them go out to a distant corner of the French Polynesian islands and come back seven hours later with smiles and novelty character-ice cream pops from Bunny’s favorite New York City bodega. Occasionally, he’ll call her Ice-Pop and chuckles whenever she makes a face. He tucks strands of wayward hair behind her ear, or back into her braid, and calls her Elsie, and then shouts and laughs hard when she mercilessly pelts him with ice.