While I was thinking that unfortunately all Kingdom fanfics are dropped, I also remembered that these are usually about Qin.
So I thought how great it would be to have a novel where the protagonist tries to fight against Zhao's destiny of being conquered by Qin.
I also thought about the character of Prince Ka, Zhao's last hope before being poisoned. The protagonist does not need to be reincarnated exactly as him, he can be an original character reincarnated as a third prince.
It would be a novel focusing on political intrigues with the King of Zhao and Prince Ka's younger brother, strategy, military command and diplomacy. The protagonist doesn't even need to be a peerless warrior.
Honestly, I've never seen a novel with this idea or anyone recommending it. But I know it has potential.