お兄さん（おにいさん）— older brother (polite or familiar)
友達 の お兄さん です。
He’s my friend’s older brother.
お兄さんおにいさん
older brother (polite or familiar)
おにいさん
accent [2]In detail
Words
友達tomodachifriend
のno(possession: ’s)
お兄さんoniisanolder brother
ですdesu(polite sentence ending)
Kanji
兄ケイ・
Use お兄さん politely for someone else’s older brother, or when addressing your own. When speaking about your own older brother to outsiders, 兄 is usual.
Coco-sensei