If Ichigo becomes a female hollow, her relationship with her father would be very interesting. Her father, who has his own secrets regarding Hollows, might have a more complex reaction. He could be both worried and a bit proud of her new powers. Her friends like Tatsuki might be a bit scared at first but then try to accept her for who she is. Also, Ichigo's relationship with the Soul Society might become more strained as they may view a female - hollow Ichigo as a more unpredictable factor.
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.
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.
If Ash were turned into a female, his relationship with Misty would likely change significantly. Misty might see her as a sister figure more than before and they could have more in - depth conversations about girl - related things in the Pokémon world, like the best places to catch certain water - type Pokémon that are more appealing to female trainers. His friendship with Brock would have a different dynamic too. Brock might be more hesitant in his usual flirting ways as Ash is now female. And his other friends might be more curious about this new Ash and how she approaches Pokémon training differently from before.
Her relationship with her family could also be different. Her parents might treat her more delicately or have different expectations. And her siblings might tease her in new ways or be more protective. Also, her relationship with her enemies could change as they might underestimate her or be more hesitant to fight a girl.
His relationship with his friends would be very interesting. For example, Orihime might be more worried about his Hollow side and try to help him keep it in check. Chad could see his Quincy power as a new way for them to fight together. And Uryu might have a complex relationship with Ichigo as he is now also part Quincy. As a Shinigami, Rukia would be there to guide him in the ways of the Soul Society while also being curious about his other powers.
His relationships with his human friends might become a bit strained at first. He would be spending a lot of time at the academy, away from them. But with his new Shinigami friends, he would develop strong bonds. They would understand his new life and challenges better. For example, he might have a mentor - like relationship with an older student or a friendly rivalry with someone of equal strength.
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.
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.