Perhaps in the fanfiction, the Titan of Earth has a connection to Percy's family heritage that he was unaware of. This discovery leads Percy on a journey to understand his own powers better. He has to face challenges like dealing with the Titan's minions who are trying to use Percy to fully revive their master. Along the way, he also has to balance his normal demigod life and relationships.
One idea could be Percy having to face an ancient sea curse that was long forgotten. Maybe it was set by a powerful Titan before his time and it starts causing strange phenomena in the ocean, like ships disappearing without a trace. He has to team up with some new sea creatures he's never encountered before to solve it.
Perhaps Percy, as the God of the Earth, has to plant the seeds of a new magical forest to restore balance to the world. But an evil force is trying to stop him by sending monsters to attack him and the forest he is trying to create. He has to use his earth powers to defend and also enlist the help of nature spirits like dryads. He also discovers that this new forest has a connection to an ancient prophecy that could change the fate of the world.
One interesting plot idea could be exploring the untold stories of the minor characters in the 'Titan's Curse'. For example, what the satyrs were up to when they weren't with Percy and his friends.
One idea could be Percy discovering new powers inherited from his Titan heritage that set him apart from other demigods. For example, he might be able to control time on a small scale, like slowing it down during a battle to gain an advantage.
A possible plot for a Percy Jackson Titan self - insert fanfiction is that the self - insert is a Titan who was imprisoned by the gods long ago. They manage to break free and find themselves in the modern world of Percy Jackson. Instead of seeking revenge immediately, they decide to observe and learn about the new world. Along the way, they befriend Percy and the gang, but their true identity is slowly revealed. This leads to a conflict as some demigods want to imprison them again, while others believe they can be an ally. The self - insert then has to prove their worth and intentions.
One idea could be that Percy has to hide his Titan heritage from the other demigods at Camp Half - Blood. He discovers new powers related to his Titan side that are different from his godly powers. For example, he might have the ability to control certain aspects of nature in a more primal way compared to his Poseidon - related powers.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be Percy and his friends getting trapped in a virtual game world that's a twisted version of their own. They have to use their demigod skills to defeat the digital monsters and find a way out.
Maybe Percy is sent on a quest to Atlantis because there are rumors of a traitor among the Atlanteans who plans to side with the Titans. Percy has to navigate the complex political situation in Atlantis and figure out who the traitor is before it's too late. He also has to deal with the Atlantean magic which is different from what he's used to.
One idea could be that Percy discovers a hidden realm within the world of the Wanderer. This realm has its own set of rules and challenges that he has to navigate. Maybe he meets new demigods there who have been lost for centuries.