Percy might tease Nico and Will a bit about it in a friendly way. But overall, it wouldn't change his relationship with them. He knows that the fanfiction is just the fans' imagination and not a true reflection of their real - life relationships. He would still be their friend and support them in their real adventures.
At first, Percy might be a bit awkward around Nico and Will after finding out. But as he realizes that they have no control over the fanfiction, he'd go back to normal. He'd understand that it's a part of the fandom and not something that should affect their relationships. In fact, he might even start to see it as a way to bond with them, joking about some of the wilder ideas in the fanfiction from time to time, but always making sure they know he respects their real - life personas and relationships.
It might not have much of an effect at all. Charlie is quite independent and focused on his own work with dragons. He might just see it as a bit of fun and not let it impact his relationship with Harry or Ginny.
It could bring them closer. If they both enjoy a particular fanfiction, they would have something new to bond over. They could discuss their favorite parts, the characterizations, and how it relates to their own experiences.
It could make their friends tease them a lot. For instance, Krillin might make some good - natured jokes about it, which could initially make Videl and Gohan a bit embarrassed.
If Percy looks at Medusa in a fanfiction, it could strain his relationship with Annabeth. She might be worried that Percy has been turned to stone or that he's been affected in some other negative way. She could become overprotective or even a bit angry at him for getting into such a dangerous situation.
If Percy wished for Annabeth to always be safe, it would likely strengthen their relationship. Annabeth is often in danger, and this wish would show how much he cares for her. She would also feel more secure in their relationship knowing that Percy has used his one wish to protect her.
His relationship would probably force him to be more selfless. In order to protect the mortal he loves, he might have to put their needs before his own desires for power and chaos. This would be a big change for Loki as he's usually very self - centered. Also, it could make him more vulnerable as he would be opening up his heart to someone who could be easily hurt.
It could strengthen Clint and Natasha's relationship in a way. They'd know that people see them as a pair and might play into it a bit more. For the other Avengers, it could bring them closer as they share a laugh about it.
Definitely Percy. He's always getting into wacky situations himself, and having a baby Nico around would just add to the chaos. He might try to teach baby Nico how to sword - fight with a toy sword, and it would be this really goofy scene with Percy making big, exaggerated moves and baby Nico just giggling.
His water - controlling power would be a huge advantage. For example, during naval operations, he could manipulate the sea to create safe passages or disrupt enemy ships. Simple as that.
His water - controlling powers would make him an excellent teacher for spells related to water. He could demonstrate how to manipulate water in ways that normal wizards might not think of. For example, he could create huge water sculptures during class to teach about the properties of water in magic.