If Snape loses his memory, initially Harry might be very confused. He's used to Snape being his enemy. But without his memories, Snape might not show the same animosity towards Harry. Harry could even feel a sense of pity and try to help Snape regain his memories. Their relationship could shift from one of hatred to a more complex one of trying to understand and help each other.
If Voldemort loses his memory, Harry might initially be extremely suspicious. But as he sees Voldemort's new, innocent state, he could start to feel a bit of pity. He might still be on guard, but not as hostile as before.
Snape's relationship with Harry could become more complex. He might start to see Harry as more than just Lily's son. As headmaster, he has to ensure Harry's safety and development. This could lead to some awkward but necessary conversations between them. Snape may also use Harry as an example to show the other students what it means to be brave and stand up against evil, which in turn makes Harry see Snape in a different light.
It would be extremely complex. Harry might initially be in disbelief and struggle to accept Snape as his father. Snape, on the other hand, would probably be very strict but also deeply protective in his own way.
His relationships would be turned upside down. His friends would be heartbroken and might have to re - introduce themselves to him. Some might become overprotective, while others could be distant, not knowing how to handle this new Percy.
He might become more arrogant. With royal status, he could develop a sense of superiority over others. For example, he might look down on his students more than he already does in the original story.
Voldemort might be initially thrown off by Harry's change. He may see Harry as a less threatening figure if he becomes a girl, thinking that the 'chosen one' prophecy might not apply in the same way. But then he could also see Harry as an even more interesting target, as a female 'chosen one' would be something new and unexpected in his view of the wizarding world's power dynamics.
In some fanfictions, Snape might share some of his knowledge about the wizarding world's secrets with Harry. Maybe he tells Harry about certain spells or magical artifacts that could help Harry in his fight against Voldemort. This act of sharing knowledge is a way of being nice as it gives Harry an advantage in his battles.
The relationship might turn into one where Harry has to constantly remind Dumbledore of who he is and their shared experiences. Dumbledore, in his senile state, could forget important things about Harry like his role in the fight against Voldemort. Harry would then have to patiently re - introduce himself and the situation. This could be frustrating for Harry at times, but it could also deepen his understanding of Dumbledore as a more human and fallible figure.
Dumbledore might be more guarded around Harry. He would be aware of the potential danger if Harry were to embrace the darker aspects of Salazar's legacy. He would still try to guide Harry, but there would be a new layer of caution.
The relationship would start off rocky. Snape would be resistant to Harry's kindness as he has always seen Harry as James Potter's son. But Harry's persistent efforts to understand and help Snape would gradually break down Snape's walls.