In a fanfiction, it could be that there is a prophecy that involves both Percy Jackson and the Red Dragon Emperor. They are brought together by the Fates. The Red Dragon Emperor might be seen as a key figure in the Percy Jackson universe's future battles. Percy has to convince the Red Dragon Emperor to side with the demigods against the Titans or other emerging threats. Along the way, they encounter various challenges that test their loyalty and friendship, and they also discover new aspects of their powers.
Well, perhaps in the fanfiction, the Red Dragon Emperor's power gets out of control and Percy, with his experience in dealing with mythical powers, has to step in. He could use his water - based powers to cool down the Red Dragon Emperor's fiery and chaotic power. This could lead to a deep friendship between them as they learn from each other's strengths and weaknesses.
They might start off as rivals. Percy, being used to the Greek mythological world, could be skeptical of the Red Dragon Emperor's power. But as they face challenges together, like a horde of mythical beasts attacking them both, they start to respect each other's abilities and work as a team.
Perhaps the fanfiction could focus on Percy's relationships in his role as emperor. He could form alliances with other demigods in Rome. His relationship with Annabeth might also be affected. She could visit him in Rome and they could work together to solve problems, or there could be tension due to the differences between the Greek and Roman worlds.
One possible plot could be that Percy, with his natural heroic instincts, discovers a hidden world of dragon riders. Maybe he stumbles upon a dragon egg during one of his quests. Since he has a connection with water and dragons are often associated with elements, he could find a way to bond with the newly hatched dragon. This would lead him to learn the ways of the dragon riders, facing challenges from those who oppose a half - blood like him becoming a rider.
Well, a plot could involve the dragon being cursed. Percy discovers the dragon in a weakened state. The curse is related to an ancient grudge between two minor gods. Percy has to journey to find these gods and convince them to lift the curse. Along the way, he faces challenges like the dragon's uncontrollable outbursts which put him and his friends in danger. Or perhaps the dragon has a hidden lair filled with treasures that are actually powerful artifacts. Percy has to enter the lair, deal with the dragon's defenses, and retrieve the artifacts to stop a dark force from using them.
Maybe in the fanfiction, the zoo is a place where the gods have hidden some of their lost magical artifacts. Percy, being the son of Poseidon, senses a strange water - based magic near the aquarium section. He starts to investigate with Annabeth. Along the way, they face challenges from zoo security (who are unknowingly being influenced by a minor god who doesn't want the artifacts found) and various magical traps set around the exhibits.
A plot could involve Percy being sent to Forks on a quest. He discovers that there's a powerful artifact hidden in the area that could cause chaos if it falls into the wrong hands. The vampires and werewolves in Forks are also after this artifact for their own reasons. Percy has to navigate the complex relationships between these two groups while also trying to keep his true identity as a demigod a secret. Along the way, he forms an unlikely friendship with Jacob, who helps him understand the ways of the werewolves.
One possible plot could be Percy arriving in the DxD world and being mistaken for a new, extremely powerful devil. He then has to navigate the complex politics of the devils while also trying to find a way back home. Along the way, he uses his demigod powers in unique ways against the various threats in the DxD universe.
Well, perhaps in the fanfiction, the dragon rider is betrayed when they are blamed for a crime they didn't commit. Maybe it was a theft of a powerful magical item. The real culprit sets up the dragon rider, and Percy, believing the false evidence, turns his back on the rider. The rider then discovers the real thief's identity and has to fight against both the false accusations and the real villain to clear their name and reconcile with Percy.
One idea could be Percy having to form an unlikely alliance with the Dragon King to defeat a common enemy, like a new and powerful Titan. The Dragon King might have his own motives and secrets that Percy has to figure out during their partnership.
One possible plot could be that the Volturi from Twilight discover the existence of demigods from the Percy Jackson world. They see the demigods as a threat to their vampire supremacy. Percy and his friends have to team up with some of the more friendly vampires, like the Cullens, to fend off the Volturi. This would bring together the magic and powers of both universes in an epic battle.