He could have adventures that involve mentoring the younger demigods. Since he's an adult, he has more experience. He might lead them in more complex quests, like exploring uncharted parts of the mythological world that are too dangerous for the younger ones alone.
He could be involved in some really cool quests. Like finding some ancient artifact that's hidden deep within Olympus. He'd probably make new friends among the minor gods and goddesses. And of course, there would be the constant threat of some ancient evil trying to take over Olympus, and he'd be right in the middle of the fight to defend it.
He could have adventures in London's underground tunnels. There are so many mysterious and spooky areas down there that could be full of monsters. Maybe he'd discover an ancient Greek temple hidden beneath the city that's been forgotten for centuries.
He could have adventures involving other sea - related deities. Since Thetis is a sea - goddess, he might interact more closely with her kin. For example, he could be sent on a quest by Thetis to retrieve a powerful artifact from the deep sea that is guarded by a fearsome sea - monster.
A new main antagonist could be a forgotten or banished god. There are many minor gods in Greek and Roman mythology that haven't been explored much. One of them could be angry at the demigods for getting all the attention and decide to cause chaos. For example, a god of misfortune who decides to curse the demigods with a series of bad luck that leads to dangerous situations.
They could have an adventure where they have to retrieve a lost artifact that is important to both their parents. Percy could use his ability to control water to navigate through underwater caves or obstacles, while Annabeth's knowledge of architecture and strategy would help them figure out the puzzles and traps along the way.
With the younger demigods, he would be more of a father figure. He would offer guidance and protection. For instance, he could teach them how to control their powers better, just as Chiron taught him when he was younger. His approach would be more mature and strategic.
Perhaps in this fanfic, Percy is raised as a sort of prince on Olympus. He could be given tasks by the gods to prove his worthiness to be among them. This might include going on quests that are not just for the safety of the mortal world, but also for the stability of Olympus itself. He would also have to navigate the complex social hierarchies among the various gods and goddesses.
Well, the characters might face new threats that emerged after the giant war. For example, some leftover magical creatures that were once under the giants' control could now be causing chaos. Also, they could have to deal with political unrest within the Olympian world as different gods vie for power in the post - war situation. There could be new quests to retrieve powerful artifacts that were lost during the chaos of the giant war. And of course, there could be new relationships forming among the heroes, both romantic and platonic, which would add more depth to the story.
A lesser - known but really interesting fanfiction is 'Annabeth's Quest for Wisdom'. This story follows Annabeth as she goes on a solo quest to gain more knowledge and wisdom. It shows a different side of her character, her determination and her thirst for knowledge in a very engaging way.
It's about the adventures of Percy Jackson and his friends in the world of Greek and Roman mythology. They face various challenges, monsters, and quests related to the Olympian gods.