Alot of ppl are saying there's no point of the incest tag if they aren't even blood related
But then eromanga sensei exits One of the most infamous incest animangas out there.
If the mangaka's focus on the taboo that these two are "siblings" which is preventing them from getting together then I think the incest tag should be included.
Im still not fond of incest myself tho i just wanted to say that