noun
A person who believes in something, often used in religious, philosophical, or fandom contexts. The English loanword carries a slightly more emphatic or modern nuance compared to native Japanese equivalents.
彼は熱心なビリーバーだ。
He is a devoted believer.
そのバンドのビリーバーたちが会場に集まった。
Believers of that band gathered at the venue.