I think there are some connections between Aldebaran and the Oni twin sisters. That's my theory :
In the Arc 3, after Subaru was severely beaten by Priscilla, Al asked Rem (he named her Ram) to take care of Subaru. But Rem answered him she's not Ram but Rem and Ram is her sister's name. Then, Al questioned her if Ram was still alive. Rem approved (she thought he had already met her sister somewhere before).
After learning that, he gonna fucking mad. In my opinion, he was persuaded she's dead, killed by him more exactly. And also, he lost his left arm and his face was burned during his fight against her. However, there is only one possibility they can fight each other. That means before Roswaal hired both twin sisters or rather during the Oni…Read more >