They are each other's "ordained punishment." Thousands of years ago, the female protagonist was a witch who protected the dynasty but was let down by the king (the male protagonist in his previous life) and sentenced to death; the male protagonist was an emperor who made a big mistake out of suspicion. The law determines that they need to go through ten lifetimes of love tribulations and repay the cause and effect in the most painful way. And this life is the last one, and also the one with the greatest changes.
I hope everyone will support me.