Crusader Kings III

As the last fellow mentioned, you need to begin as Vratislav Přemyslid in 1066, remembering to choose Ironman Mode! You start having de Jure claims, so careful expenditure and politics will enable you to vassalize for strength and to create the Duchy of Moravia in a short amount of time.

You are already a vassal of the Holy Roman Empire and can vote for yourself in elections, through the use of Diplomacy perks I was able to forge enough alliances and friendships to garner support in a fairly short amount of time. Depending on how you like to play, you can then use conquest, intrigue tricks or diplomacy to either be voted into leading the Empire, to fight for ownership or to simply kill off the other opponents and heirs!

Of course by this point you will have already formed the Kingdom of Bohemia as soon as the option arose when you had Moravia and the funds, so once you are declared Emperor the achievement should pop straight away :)

It isn't the easiest of achievements in the game, but does allow flexibility to attain depending on your play style :)

You’ll have to begin your game controlling Vratislav Přemyslid, in the year 1066; and from there, manage your Dynasty until you achieve control of the Kingdom of Bohemia first, then the Holy Roman Empire. This will take you some time, but luckily, you control the de Jure lands that form the Kingdom of Bohemia as your game begins: you’ll just have to collect enough Gold and form the Moravia Duchy before you’re able to move on, though. From there, you’ll have to climb your way through until you get to the throne of Holy Roman Emperor you’re a vassal of.