Both Lumine and Aether have to be in the game since they are MCs of the game but both can't share the same faction since they are on opposing sides. So the very solid theory in my eyes is that both can't be town together and this is deadset. The others just talk out of preferences but in the game you can chose between Lumine or Aether, the twins to be your playable character to start with. The other becomes the main antagonist for the time we are currenly set in. So yeah that is what we are figuring out now on which side Aether is and on which side Lumine could be.