We know that the twins traveled between worlds following the destruction of their civilization. I’m just thinking about for what purpose, all of which might just be answered by the Project ARK speculation that’s existed since this game came out.

I feel like it’s pretty reasonable that they were traveling between worlds looking for habitable planets. Something that I really can’t shake though is that, whatever reason they were traveling, the twin we choose is meant to be the backup plan for Abyss Twin in case things/their “mission” go terribly wrong. As in they were never meant to be awake at the same time literally for survival, kind of like how the people who know the Coca-Cola secret formula can’t fly in the same airplane.

So Abyss twin traveled Teyvat for centuries, keeping MC in their back pocket just in case. Whatever happened that prompted the Abyss Twin to wake up MC must have not only been emergency escape, but also a Plan B in case of catastrophic failure or death. I don’t know if any of that makes sense (probably not!), but TL;DR the MC is almost like a backup copy of the Abyss Twin who the Abyss Twin must “boot up” in a dire emergency in order to secure their mission’s success—or in case Abyss Twin becomes corrupted. Genesis Pearl much?