sounds like it could be either
https://www.mangago.me/read-manga/pygmalion/
https://www.mangago.me/read-manga/gleipnir/
Your description reminds me a of Gleipnir, but as far as I remember, there is no apocalypse and the person who transforms into a mascot suit is a boy. https://www.mangago.me/read-manga/gleipnir/
Thank youuu it's the first one!
Thank you I found it. It's pygmalion
There was an apocalypse happening and one girl (ig she's still a kid) turns into this bunny suit? Like a zip up suit kinda. I think they considered her a monster but she was on her right mind. It's been over 5 years since I've read it so I don't remember vividly sorry.