妹さん（いもうとさん）— younger sister (someone else’s)
友達 の 妹さん です。
She’s my friend’s younger sister.
妹さんいもうとさん
younger sister (someone else’s)
いもうとさん
accent [4]In detail
Words
友達tomodachifriend
のno(possession: ’s)
妹さんimoutosanyounger sister
ですdesu(polite sentence ending)
Kanji
妹マイ・
妹さん is a polite way to refer to someone else’s younger sister. When speaking about your own, use 妹 without さん.
Coco-sensei