This is certainly what could be the case, except it isn't. It was decided in 1949 what the current understanding of democracy in Germany is. You could of course decide to define democracy as broad so that it also encompasses the Athenian democracy, but that is not what we currently mean when we speak of a liberal democracy.

If party A, being labeled as communist by party B, and party B, being labeled as fascistic by party A, both agree, as well as all other parties in-between, that you are a threat to democracy, maybe you are.

If you are looking for a party that labels itself democratic and all others anti-democratic, you need to look at the AfD themself.