Well, with his friends, they would have to adjust to his new state. Percy would rely on them a lot more. Grover might feel an even stronger need to protect him. And with other demigods, some might tease him while others would feel sorry for him. His relationship with the gods could also change. Some gods might find it amusing and not take him as seriously, while others might see it as an opportunity to manipulate him in his vulnerable state. His romantic relationship, if he had one, would be put on hold. His partner would have to wait until he's back to normal or might develop a different kind of affection, more like towards a little brother or something.
Well, Percy's relationships would be in upheaval. In the case of his friends, the dynamics would shift. His male friends might have to reevaluate how they interact with him. For example, they might be more cautious about physical contact or their language. His female friends could either embrace her new form and become closer, seeing her as one of them now, or they could be jealous if Percy in his new female form gets more attention. And in terms of romantic relationships, if Percy was interested in girls before, he might now find himself attracted to boys, which would completely change the nature of his love life.
He'd probably be more innocent. The snobbish and often cruel Draco we know would be replaced with a more naive and curious version. He might not have the same prejudices as he does as a teen or adult.
His relationship with Tails would be strained. Tails would be confused and a bit scared at first. Sonic would have to hide his new vampiric urges from Tails, which would create distance between them. With Knuckles, there might be more of a distrust as Knuckles is very protective of their world. Knuckles might see Sonic as a threat now that he's a vampire.
With his love interests, if he had any, it would be completely different. If he was interested in a girl before, she might see him as a rival now. And if there were guys who had a crush on him as Superboy, they might be confused or even more attracted to him as a girl. Also, his relationship with his family members, like his father figure, might change as they adjust to his new gender.
In a fanfiction where Natsu turns into a girl, his relationships would be turned upside down. His relationship with his friends would be filled with awkward yet endearing moments. His male friends might have a hard time adjusting at first, but gradually they would accept the new Natsu. Natsu's relationship with the female characters would also change. He might find himself being included in more girl - only activities, which would strengthen his bonds with the female members of the guild. And his relationship with the outside world, like with other guilds or villains, would also be different. Enemies might underestimate him because he is now a girl, but Natsu would prove them wrong with his strength and determination.
If Naruto was turned into a monster in fanfiction, his relationship with the village would change drastically. The villagers who have finally started to accept him as a hero would once again be fearful. His friends would be divided in their reactions. Some, like Shikamaru, would immediately start thinking of ways to solve the problem. Naruto's relationship with his mentor, Kakashi, would be put to the test. Kakashi would have to balance his duty to the village and his loyalty to Naruto. And Naruto himself would feel isolated, which could further impact his relationships as he might become more withdrawn in his monster form.
Well, he might lose all his skills and knowledge at first. For example, he probably wouldn't be able to handle his sword as well as before. He could be really confused about his new small body and the world around him that now seems so much bigger. His friends would have to take care of him like a real little kid, feeding him, dressing him, and making sure he doesn't get into too much trouble. Maybe he would also start to see things from a completely different perspective, like being more innocent and curious about simple things that he used to take for granted.
Well, with his mother, Sally, it would be a very different dynamic. Sally, who has always been proud of the grown - up Percy, would now have to mother him all over again. She would be more protective and might even try to keep him away from the dangerous demigod world for a while. As for his enemies, they might underestimate him at first. But as they realize that even as a kid, Percy still has some of his heroic instincts, they would start to see him as a threat again. His relationships with the gods would also shift. Some gods might pity him and be more lenient, while others might see it as an opportunity to manipulate him more easily.
If turned into a kid, Deadpool's personality would lose some of its edge. He'd be more impulsive in a child - like way, not thinking about the consequences as much as he does as an adult. His love for chaos would remain, but it would be more like a child's playfulness. He might also be more vulnerable in a sense, showing emotions more openly like a kid does.
His relationship with Rukia would be different. Rukia might be more protective of Ichigo in her new form, seeing her as more vulnerable. And with Uryu, he might be more hesitant to interact with Ichigo as a female hollow at first, due to his Quincy beliefs.