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.
If Sonic turned into a vampire in fanfiction, his relationship with his friends would be drastically different. His friends would be shocked and perhaps a little afraid of him. Sonic would feel isolated as he tries to keep his new condition a secret. Amy, who has a crush on Sonic, would be heartbroken and conflicted. She might still love him but also be scared of what he's become. Sonic himself would be more withdrawn from his friends as he battles his new vampire nature and the potential harm he could cause them.
Well, Sonic's relationships would change significantly. For example, his relationship with his friends would become complex. His friends might initially try to help him, but as time goes on and Sonic's vampiric traits become more pronounced, they could start to fear him. Sonic would also have to deal with the fact that he is now different from them. He might feel like an outcast, even though his friends still care about him. He could also form new relationships with other vampire characters in the fanfiction, which could further complicate his relationships with his old friends as they might not understand or trust these new allies of Sonic.
His relationships would change drastically. His work colleagues, for example, would notice his different behavior. He might start to work at night and avoid daylight. His relationships with other vampires could also be complex. He could form alliances with some vampires who are more sympathetic to his situation, while others might see him as an outsider. In his social circle, he would become a mystery to those who knew him before, and he would have to find new ways to interact with people.
Her relationships with humans would likely become strained. Humans might be afraid of her now that she's a vampire. Her romantic relationships could also change. If she had a human lover, they might have to reevaluate their relationship. And her friendships with other vampires could shift too, depending on how they view her new status as a turned vampire.
Her relationships with her human friends will surely be affected. They might be scared of her at first, or she might be afraid of hurting them. So she may start to distance herself from them.
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.
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.
They might become more withdrawn. Since vampires are often associated with secrecy, the maknae could start to keep their thoughts and feelings to themselves more. For example, they may not share their newfound struggles with bloodlust with their friends right away.
Percy might become more brooding. As a vampire, he's now part of a world that's often associated with darkness and mystery. He may also become more possessive, which is a common trait among vampires. For example, he could be overly protective of his territory or the people he cares about.
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.
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.