This one is a famous theory most fans wonder about.

Is HRE really Germany?

In my opinion, yes. He is probably Holy Roman Empire. I will not say that the fact his appearance resemble the old empire, but use history as well.

When the Holy Roman Empire was defeated and was dissolved, two countries were created or born: Bunderepublik Deuschtland and Republicca Italiana; or in English, Republic of Germany and the Italian Republic.

Does it make sense? Of course. History does not back up this theory, but it makes sense.

Now, to Hetalia version.

Italy was with HRE when he was a child, right? Well, when he left to battle France, he lost and was killed and had amnesia, according to fans. In that case, HRE does not know or in fact, remember his childhood love. When Germany was born, Prussia was happy. He was so sad when HRE lost memory. When Germany got older, he realized Italy was his liebe, I imagine him running to Italy and hugging him, then confess that he's HRE.

When I asked this to Mikokori2, my friend in the Yandere Simulator wiki, who is a Hetalian, she said that in a AU she made that Italy was HRE and the personalities were a little bit altered,
But Germany is still Prussia's brother. When they met each other again, Italy finds Germany in a box of potatoes.

Now, many people will disagree with me, but some fans who know history well might agree with me. I'm sorry if this is short.