User blog comment:Mitchell20/Nauibotics/@comment-294304-20180616215134

There is actual game script (see here where Mikoto explictly says that Arete is her older sister. Azura is Arete's daughter, so its not hard to put two and two together.

Folks have raised the point that this is a pointless addition, as this reveal just comes and goes and the characters barely react to it, but Fates' writing is notoriously bad so this is hardly anything new.

Is there anything else we need to discuss?