As it turned out, Aishia was truly the last surviving member of the Valkyrie race, an original member of Asgard.
She was born shortly before the Great War began, and she didn't have nearly enough time to grow her strength before the flames of war encapsulated the universe. As the youngest, she was hidden and protected by the entire race, ensuring her survival over the corpses of her brethren.
Aishia never left this unnamed world since then. She grew her strength by battling against the Nox on the surface and became a true powerhouse who could hold a say in the most important matters.
The decision to have her play his wife was actually her own. In truth, she was a close friend of Bai Xieren, who filled her in on Damien's role.