When he first saw HRE's reincarnation, he felt a little passive aggressive towards him. The only bonding they do is sword train and ways to fight in the war. Prussia never treated his wounds when he was little nor celebrated his birthday. Until that day, when Prussia visited Fritz's grave he hadn't noticed that Little Germany followed him with fresh bouquet of flowers. He said "I'm sorry that I cause any trouble in your life. If it wasn't for me...you'd be the best person in the stories I've read about you..."
And that's when Prussia realized that he regret what he did to him....
