His personality would likely become more protective. Since Cerberus is a guardian, Percy might feel an intense need to protect those around him more than ever.
In a fanfiction where Percy Jackson turns into Cerberus, a lot of things could occur. Since Cerberus is a guardian of the Underworld, Percy might find himself in the Underworld without really knowing how he got there. His friends would be really worried about him. He might start to discover new powers that come with the Cerberus form. For instance, he could have enhanced strength and a powerful sense of smell. But he'd also face challenges like communicating with his friends, as he can't just talk normally in that form. He'd have to figure out a way to let them know it's him.
Well, his confidence might shift. As a woman, Percy could be more cautious at first, having to deal with different social expectations. But he could also become more empathetic. Since society often expects women to be more in tune with emotions, Percy might start to pick up on the feelings of others more easily.
He might become more fierce. As a dragon, he has the physical power to match his temper at times. He could be less patient with those who oppose him.
Her personality change could be influenced by the new experiences she has as a girl. For instance, she could be more fashion - conscious, which might seem superficial at first but could actually lead to a deeper exploration of self - expression. This newfound interest could make her more open - minded to different forms of art and creativity. Additionally, she might develop a more collaborative personality. Instead of always being the lone hero type as a boy, she could start to work more closely with others, especially other female characters, sharing ideas and building stronger relationships.
The main characters would be Percy Jackson, who has to deal with the implications of being the son of Cerberus. Then there's Cerberus, whose relationship with Percy is the central concept. Chiron, the centaur at Camp Half - Blood, would also be important as he's always been a guide for Percy. And don't forget about the other demigods at the camp. They would react to Percy's new identity in different ways, some with suspicion, some with curiosity, and their reactions would be part of the story.
His relationship with Annabeth would be different. She might have to get used to Percy being a pegasus. There could be some initial awkwardness, but also a deeper understanding as she sees him in a new form.
One interesting plotline could be Percy having to team up with Cerberus in some way. Maybe there's a threat to the Underworld that only they can stop together. Another could be Percy exploring his new 'son of Cerberus' identity and how it affects his relationships with his friends at Camp Half - Blood. For example, some might be scared or distrustful of him at first.
One possibility could be that Percy, as a new god, would have to deal with the complex politics of Olympus. He's always been an outsider, and now he'd be thrust into a world of power plays and ancient rivalries. Maybe he'd try to change some of the archaic rules that the gods have held onto for centuries.
One idea could be that Percy turns into a dragon to fight a powerful sea monster. Since he has his connection to water, as a dragon he could breathe a sort of water - based fire or ice that freezes the water around the monster, trapping it.
His personality would likely experience a shift towards a more solemn and responsible demeanor. With godly powers come great responsibilities. Percy would no longer be able to act as carelessly as he did as a demigod. He might become more reserved in showing his emotions, especially as he realizes that his actions as a god can have far - reaching consequences. Also, his loyalty might be tested as he has to balance his new divine status with his relationships from his mortal days.