"But everything changed when the Yandere Brainrot Nation attacked."
I don't even know if I'll write these ajkdnajkdsnajk. But this post will serve as a Masterpost for ideas.
Idea one: Royal AU where the Reader is a princess of a defeated Kingdom. In order to secure peace (and a way to ensure your people's obedience), you are to marry one of King Crepus' sons, but in reality, you are just a glorified prisoner.
You were meant to be nothing but a pawn, little did King Crepus know that you were to become his nation's greatest threat, as both his sons fall madly in love.
Idea two: In the middle of Liyue's darkest period of terror, the legend of a bloodthirsty Yaksha terrorizes the land. The little village you grew up in is growing weaker as raids continue, and you become the victim of their despair and superstition.
So they offer you as a sacrifice for the Yaksha to take.