Not to turn this into a tranny friend support group, but yeah, same here.
He liked anime (first sign, I know), but then he got into Osu. Which was fine, we all have our hobbies, he likes rhythm games, I like racing sims. But as time went along we went from watching Jojo to watching shit like K-on and Love Live (or whatever slice of life anime girl shit they're called), and then he began making remarks like "Man, imagine if highschool was that easy", which in hindsight was a massive red flag. Then he began to grow his hair out, which is fine, I have long-ish hair because I'm an eboy on instagram, but he grew it far past that, claimed he was "trying a metalhead look". But metalheads don't dye their hair marine blue. After that it was a descent, him "ironincally" getting a maid outfit for the "lols", then commenting about "Felix being his waifu", and so on. Worst part was he was growing slimmer too. He used to do parkour and running, so he used to be lean, but very fit. Like his muscles weren't huge, but he was all muscle, little body fat, so he looked normal if not skinny. Then he just stopped working out, and grew into just a tall, lanky dude with no muscle.
I'm not saying it was anime, but it has to be some mental disease. What would make a guy go from someone who was fit, masculine, and got laid more than a blowupdoll in a prison turn into a shy, introverted, and this hurts to say, pathetic trans "girl"? He went from a guy I looked up to, to somone I pity so much it hurts.