big fan; great fan
Emphatic way to say you are a devoted admirer of a person, group, work, or activity. Common in casual conversation.
I'm a big fan of that band.
彼は子どもの頃から野球の大ファンだ。
He's been a huge baseball fan since he was a kid.
Compound of prefix 大 (だい, 'big, great') and loanword ファン (from English 'fan').