First of all, I only saw the Drifters anime years ago and read a little about the fandom. Unfortunately, the manga that started in 2009 only has just over 80 chapters and probably only a few fans still follow it. That's why I prefer the fanfic to be AU.
Regarding Emperor Nero, I thought about a person reincarnating in Nero's body. Look, Drifters has two 'gods' playing a game of chess with the fate of a world, I wouldn't be surprised if someone reincarnating in someone else's body happened.
I even thought about other historical figures, but I remembered that someone will always come up saying "Fun fact,..." or "Actually,...🤓" complaining about how that person behaved in real life. So I gave up and chose Nero, the author can even take advantage of this to make some memes.
The good part of this being AU is that you can add whatever you want. New human nations, more historical figures and so on. I would like the MC to meet the original three main characters after a good while, when he has already established a kingdom. The main tags for this story would be Kingdom Building and War Strategy, the rest is up to the author.
There isn't much to invent for the ending, it would just be defeating the Ends and maybe conquering the World. And please do something with Scipio and Hannibal, I particularly didn't like how the anime treated these two legends.
I don't even care if you thought this story was bad, I just hope it inspired someone to write a fanfic. 😘