Its been a long time and only read the description. So here is what little i remember.
The protagonists are an empress and emperor if i remember corectly (they were of hight rank at least). The empress loved the emperor but the emperor hated her. She died (not of natural cause) and came back to the past. She is i think still obsessed with him but here is a twist. The past she returned to is in another timeline. In this timeline the emperor is obsessed with the empress but the empress doesnt like him back (the opposite of before) . So now the regressed empress (who is obsessed with the emperor) is in the same timeline with the emperor that is obsessed with the empress.
That all i remember from the description.
I don't get it. If Cheng Qianmo want to be teacher what does it matter even if he loses? What matter is the knowledge that he has and is supposed to teach to others so there is no point in a duel with combat, or am I missing something here. It would change if it was a knowledge duel thought.