여동생은

younger sister

→ 여동생
phrase Rare #31,662
younger sister 은 marks the younger sister as the topic of the sentence.
KO: 여동생은 학생이에요.
EN: My younger sister is a student.

여동생은 선원들이 붙인 농담 섞인 별명 이었다.

“Little sister” was a teasing nickname the sailors had given her.

어머니와 여동생은 죽었다고 하더군

I was told that my mother and younger sister had died.

— 이반의 어린 시절 (1962)