noun
super otaku; hardcore geek
Slang term for someone who is extremely passionate and deeply invested in their hobby, especially anime, manga, games, or idols. Often used self-deprecatingly or with a mix of pride and humor.
彼はアニメのガチオタで、毎週20本以上見ている。
He's a super otaku when it comes to anime; he watches over 20 shows a week.
ガチオタの友達と一緒にコミケに行った。
I went to Comiket with my hardcore geek friend.
A compound of the slang prefix ガチ (from ガチンコ, meaning 'serious' or 'real') and オタ (short for オタク, 'geek' or 'enthusiast').