The "main" avatars i've had over the years are, in order:
Moka from rosario+vampire in her vampire form
This was in my very early days on osu, before i became active in the community/on the forums. This was just a shitty screenshot i took of the ending of the anime i think lol. Most people who knew me even back then probably either have never seen this one or don't remember it if they have.
White rock shooter
This was my avatar during my active period (2012-2015) so the one most people who knew me will remember.
Some cyber gothic girl
This one i used mostly during the time that i was less active, from around 2016 until 2018.
And my current one, zesshi zetsumei from overlord.
I've been using this one since 2018 now, sometimes swapping off for a short time but then i come back to it again.
Other than that i've had many avatars that i've held for a couple of days to a couple of months at a time, a lot of them being collab avatars too.