[7Th]

Originally Posted by Divino

Spoiler for spoiler:

How does she care more for Eden if she literally betrayed him and chose Kouga is wish to destroy the ruins instead? What looked like concern was probably just guilt.

Also Shaina never mentioned that Aria was Kouga is sister or that they were related.
I think at least a "you share the same blood" would have been more clarifying.
They might be the same species or from the same planet but they aren't siblings or twins until they explicitly state that it is so in the anime.

Spoiler for Episode 24:

Destroying the ruins isn't Kouga's will; it's her will. Aria was worried about Eden because she said that he was the only person that ever cared about her while she was trapped in Mars' tower.