Responses
It could probably mean “Noona” not literally sis as sibling
I would assume he's calling her Noona, doesn't necessarily mean they're related. It's what guys call women who are older + close to them in korean.
Lisa of people call the petal Noonan or hyunv.. it does not mean they are related
Wait? Sis??? What the hell? Wasn't it his fiancée? I'm not trying to be mean but the one translating.. did you even read the story??