Well, with Dipper becoming a girl in the fanfiction, his relationship with Mabel would have a new dynamic. Mabel would be all about embracing Dipper's new form. She'd be planning slumber parties and trying to give Dipper a new 'girly' identity. As for Wendy, Dipper might find himself more in tune with Wendy's interests on an emotional level now that he's a girl. Wendy might be more open to sharing her feelings with Dipper - girl. His relationship with the townspeople could also change. Some might be more accepting, while others might be a bit more judgmental. And his relationship with the supernatural elements in Gravity Falls could be different too. Maybe some entities are more attracted to his new form, while others are repelled, which would lead to a whole host of new adventures and challenges in their relationships.
His relationship with Ron would definitely change. Ron might be a bit more hesitant around her at first, not really knowing how to act. But as time goes on, they could develop a deeper, more platonic bond. It would be like Ron having a sister all of a sudden.
His relationships with male friends might become more complex. They could start seeing him in a different light, maybe with a new - found attraction or a sense of awkwardness. For instance, if he had a close male friend before, that friend might struggle with how to act around him now. With female characters, he could either form a sisterly bond or face some jealousy if they see him as a threat in terms of male attention. His enemies might also underestimate him, thinking that as a girl he is weaker, but he would prove them wrong.
His relationship with Sasuke would likely be affected. Sasuke might initially be suspicious of Naruto's new form, thinking it could be a trick by an enemy. But as time goes on, they could find new ways to work together. Naruto's new Kitsune powers could complement Sasuke's skills. For example, Naruto could use his enhanced speed as a Kitsune to keep up with Sasuke in combat.
His relationships with his male friends might become more complicated. Some might be more protective of him as a girl, while others might be confused about their feelings towards him. For example, if he had a rival before, that dynamic could shift completely.
With his female friends, there could be a shift in the dynamic as well. They might be more open with him now that he's a girl, sharing secrets and experiences that they previously wouldn't have. He could also become more involved in 'girl - only' activities, strengthening those friendships in new ways.
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 Gray might become more complicated. Gray might be more hesitant to pick fights with Natsu now that she's a girl. And with Lucy, they could become closer as girlfriends, sharing more secrets and having sleepovers. Natsu might also attract new male friends who are interested in her as a girl.
His core personality might not change much. He'd still be brave and protective. But he might be more in touch with his emotions, as society often allows women to be more openly emotional. He could also be more perceptive about the subtleties in relationships.
Her relationship with Inuyasha would be greatly affected. He might be initially shocked and even a bit distrustful since he has had his own issues with demons in the past. But over time, he could come to accept her new form and help her control her new powers.
With his mentor or teacher figure, the dynamic would shift. Instead of being the student who is learning, Robin as a kid might be more in need of basic life lessons. His friends who were used to his equal partnership would now have to be more patient and understanding. They might find his child - like innocence endearing but also frustrating at times. And his relationship with any rivals could become more complex as they might not know how to deal with a kid version of him.