In a fanfiction where Eragon turns into a dragon, his relationships would undergo significant changes. His bond with Saphira would be redefined. They might develop a new type of connection, more like siblings in a way. His human companions would need to learn to communicate with him in a different way. For example, he can no longer speak in the same human languages. His relationship with Murtagh, if he were still in the picture, could be even more strained as Murtagh might see this transformation as another advantage that Eragon has. Eragon would also have to deal with the reactions of the dragons in the wild. Some might accept him as one of their own, while others might be suspicious of his human - turned - dragon nature.
When Eragon becomes a dragon in fanfiction, his relationships are bound to shift. His family, if they were still alive, would likely be shocked. They might not recognize him at first. His friends among the Varden would have mixed reactions. Some would be in awe of his new form and power, while others might be hesitant to trust this new dragon - like Eragon. His relationship with Nasuada could become more complex, as she now has to deal with a dragon - Eragon who has different needs and capabilities compared to his human self. Overall, his relationships would be in a state of flux as everyone adjusts to this new Eragon.
If Eragon turns into a dragon, his relationship with Saphira would be very different. They might become equals rather than dragon and rider. His human friends may be initially scared or confused. But some, like Arya, might see it as an opportunity to gain a powerful ally for the fight against evil. His enemies would be more fearful of him, seeing him as a greater threat.
His relationship with Toothless would be very different. Toothless might be initially confused and a bit hesitant around Hiccup in his new form. But as time passes, they would develop a new kind of bond based on Hiccup having to adapt to being a dragon. With Astrid, it could be strange at first. Astrid might be both curious and a bit jealous of Hiccup's new dragon form. She would have to see Hiccup in a whole new light.
In a fanfiction where Issei turns into a dragon, his relationships would be in flux. His relationship with his mentors or those he looks up to might change as they now see him as a different kind of being. They might treat him with more caution or more respect depending on how they view dragons. His friendships with his peers would also be altered. Some might see him as a weapon to be used in their battles or struggles, while others would see him as a friend in need of support. Romantically, if he had feelings for someone, that person would have to deal with the fact that Issei is no longer fully human. There could be jealousy from others who might want to be with the powerful dragon - Issei, or there could be newfound admiration from those who previously overlooked him.
Suppose Percy turns into a horse. His close friends might feel a sense of responsibility to protect him, especially if he's in a dangerous area. He could form a bond with other horses, and this might introduce new characters into the story. His relationship with his human family might become more complex as they struggle to understand his new state and how to interact with him as a horse.
His relationship with Midoriya might change. Midoriya could become more protective of Todoroki as a girl, seeing her as more vulnerable. With Bakugo, there could be a different dynamic. Bakugo might initially tease Todoroki more, but as he sees Todoroki still being strong in her new form, he might develop a new respect for her.
His relationship with Pikachu would be very different. They'd be more like equals now. Pikachu might even feel the need to protect Ash more. With his other Pokemon, they might be confused at first but then develop a stronger bond as they realize it's still Ash inside.
Aang's relationship with the Air Nomads' spirits could also be affected. As a girl, she might be seen as a new form of the Avatar by the spirits. They could communicate with her in different ways, guiding her on a different path. This could lead to new alliances and ways of using air - bending that were not available to Aang when he was male. Also, her relationship with other female characters in different tribes could become more sisterly, with them sharing secrets and knowledge specific to women.
His relationship with his uncle Iroh would be deeply affected. Iroh has always been a guiding figure for Zuko. If Zuko turns into a dragon, Iroh would be worried but also proud in a way. He would search for ways to help Zuko, and their relationship would become more about Iroh protecting and guiding Zuko in this new and strange form. Zuko, in turn, would rely more on his uncle's wisdom during this time.
If a character turns into a dragon, their relationships would change drastically. For example, if it was a knight who had many friends among the other knights, they would be seen as a threat once they start to transform. Their former friends might try to hunt them down out of fear. On the other hand, if it was a character who was previously an outcast, like a bastard, their new form could give them power and respect. They could form new alliances with those who seek to use a dragon's power for their own gain.
His relationship with his sensei, like Kakashi, would also change. Kakashi would have to train Naruto to control his dragon powers. Naruto might be a bit more rebellious as a dragon, feeling the freedom that comes with his new form. But Kakashi would still be there to guide him, and their bond would transform into one that focuses on Naruto's new abilities and how to use them for the good of the village.
Well, Natsu's relationship with Gajeel could be really different. Gajeel might be more respectful towards Natsu as a girl, or he could be more competitive in a different way, like trying to prove that he's the better dragon slayer in a more gentlemanly manner. Natsu's relationship with the guild master, Makarov, would also change. Makarov might be more protective of Natsu as a girl, and Natsu might have to fight harder to be taken seriously in guild matters. In general, all of Natsu's relationships would be reshaped, with new levels of complexity and humor added to the story.