a game called i wanna be the guy

I'd say the Bleach fandom and I first joined by saying Ulquiorra is a mid character

FNAF I was wayyyy into that shit as a child

Warriors technically

Hmmmmmmmmmmm

Probs Drakenier?

i wrote a seven page essay about hatsune miku in 6th grade because i liked her so much

Fire Emblem. Read up on as much as I could pertaining to the games without playing them

Like this? Arknights.
A lot less so? Fire Emblem.

Megaman. I joined a Megaman Spriting forum in '08 and while I was there I made a couple of friends i still have today who literally changed my life.

I've never really gotten into a fandom. The only fandom I'm slightly into is Miranda Cosgrove. Well.. you could say I really got into the Ariana Grande fandom since I followed 1,500 Arianators, but it wasn't because I was a fan of Ariana Grande, I just liked their positivity and I needed that kind of vibe in my life. For a while I didn't even follow Ariana herself.

GOD I HATE IT BUT,,, Danganropa,, I even made xreader fics I'm going to vomit...

It depends on like what you could count as being really into a fandom, but if I think of it artwise I'd have to go as far back as FnaF before FnaF3 ever came out.