His character might develop in terms of his power. Without his friends to back him up, he might have to push himself to new limits and discover new aspects of his powers. He could also become more empathetic towards others who have lost loved ones, as he now fully understands that pain. He may start to see the world from a different perspective, not just as a demigod hero, but as someone who has truly suffered a great loss.
He would probably become more somber. The loss of all his friends would make him less carefree. His sense of humor might still be there, but it would be tinged with sadness.
Percy would likely become more withdrawn at first. The trauma of being the sole survivor would take a toll on his usually outgoing and confident personality. He might start to question his own abilities and whether he could have done more to save his friends.
Perhaps in this fanfic, Percy is the only survivor but he's not entirely alone. He might be haunted by the spirits of his fallen comrades who give him guidance and strength. He could use this to fight against the remnants of the evil forces that still lurk in the shadows, all while trying to rebuild the world that was shattered in the final battle.
He would likely be more cautious and distrustful. Since he's being raised by a monster, he may not have the same sense of heroism and justice that the normal Percy has. He might see the world as a more dangerous place where only the strong survive.
Percy's character could become more self - aware. Seeing his past self would make him reflect on how far he's come. He might realize that he's grown more confident and capable over time.
His character would become more confident in his artistic abilities. Apollo is the god of many arts, so Percy would likely be exposed to music, poetry, and painting. He might be more flamboyant in his actions and speech, as Apollo has a certain charm. For example, he could start using more flowery language when talking to his friends or enemies.
Percy's character would likely become more in tune with nature. He'd be more reserved perhaps, as he grows up in an all - female group. His sense of honor might be more shaped by Artemis' values, such as protecting the weak and the natural world.
His character could develop in a way that he becomes more powerful. Since Kronos is a very powerful being, Percy might inherit some latent power. But he would have to learn to control it. He would also become more empathetic towards the Titans in a sense, as he realizes that Kronos is his brother. This could lead to him trying to find a middle ground between the Titans and the gods, which would be a major shift in his character from just being a defender of the gods.
Percy's character would develop in many ways. Firstly, he'd gain a deeper understanding of the politics among the gods. This would make him more calculating and strategic. He'd also become more empathetic towards the gods' viewpoints, even if he doesn't always agree. His relationships with his old friends would change too. He might not be able to be as carefree with them as he used to be. Instead, he'd have to consider how his actions as king affect them and the entire demigod community. Moreover, his sense of responsibility would expand far beyond just protecting his friends and family to safeguarding the entire divine and mortal worlds.
Percy would likely become more confident, given the immense power he's gained from absorbing Ouranos. He might also become more solitary, as he tries to understand and control this new power within him.
Percy would likely become more diplomatic. As Hera's husband, he'd have to deal with all kinds of divine politics, so he'd learn to be more tactful in his words and actions.