The Holy Roman Empire is not a single nation but a coallition of nations in central europe in which one can have there leaders become Emporer with the support of others, You can play as The Emporer in Saxony in order to guide the nations to your whim and reforge it into a state lead by Emporers of your house and nation for all time, play as  Bohemia a powerful non German electorate in eastern europe, Austria is a powerful German electorate in the Alps with a great future, Tuscany is an Italian electorate with great potential