I don't think they are blood related. We shall see
She's adopted
Aren’t they half-siblings?
No they are not. The father of the boy "adopted" the daughter of his former friend. He became her guardian. Not blood related at all.
They’re not related by blood. It’s pseudo-incest. Father adopted her for a very specific reason revealed later on.
But... she’s ur sister (╯°Д °)╯╧╧