English loanword used in Japanese to refer to a brother, often in a casual or affectionate way, or in contexts like 'brother' in a fraternal or religious sense.
He is my brother.
ブラザー、ちょっと手伝ってくれない？
Brother, can you help me out a bit?
シスター is the parallel loanword for 'sister', directly opposite ブラザー in gender.
counter for people
big brother; elder brother · Big Brother; dictator; despot
brother complex; excessive attachment to one's brother
Borrowed from English 'brother'.