(Ok, quick author's note, if you didn't read the description, this is basically just a headcanon that I found a while ago that I tweaked to my liking. Hope you enjoy!)
Everyone always wonders about what happened to The Holy Roman Empire. Many say he was killed in battle. Well I say that's not true. Here's what really happened.
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When HRE went off to war, he fought hard, thinking of Chibitalia constantly. But one day, he got into a large accident with the artillery. This caused him to lose his memory. There was another man who was also involved in the accident that lost his too. Somehow, the memories were transferred from HRE to the other man, the younger version of Prussia. HRE remained his looks and personality, but was changed into Germany in the process.
To this day, Prussia remembers everything about Italy when he was younger, while Germany is HRE without them. He wants to get Italy back, but he knows that the best fit for Italy would be Germany, since he's truly the man he fell in love with. He endures the pain of the memories for his brother and his first love. The two he truly cares about most.