So basicly incest?
Nah I don’t think so. I think it’s misunderstanding with the translation
Oh ╮( ̄▽ ̄)╭
No, the translator F'd up. He is calling her "Noona" which is a Korean honorifc younger men call older women (but not too old) than them. The literal translation is "older sister" but its used interchangeably for relatives and non-relatives.
So basicly incest?