Story: After being too stressful of can’t finding Lumine again, Lumine came to find Aether and asked him if he wants to join the Abyss with her, told him every details about the destruction of their homeland (Which is you already know where this twin came from). Aether said yes, taking a revenge to the Archons what they did 500 years ago, ready to destroy Teyvat.
This might be original I guess TvT