Well, he could be part of a scientific experiment to understand the limits of demigod powers. Scientists in the demigod world might want to know exactly how Percy can control water so precisely. This could lead to some interesting scenarios where Percy has to cooperate with these scientists while also being cautious not to let his powers be misused. Also, what if Percy discovers that his ability to communicate with sea creatures has a scientific basis? He could start a project to document and study this form of communication, which might in turn help demigods better understand the underwater ecosystems and how they are connected to the overall balance of the world.
A possible plot is Percy being sent on a mission by the gods to study a strange phenomenon in the ocean that is affecting both the mortal and demigod worlds. He uses his scientific skills, which he has developed over time, to analyze the situation. He might encounter sea monsters that are acting oddly due to this phenomenon and has to figure out how to stop it. Or perhaps Percy is recruited by a secret scientific organization within the demigod world that is trying to find a way to bridge the gap between the magic of the gods and modern - day mortal science. He could bring a unique perspective with his experiences as a demigod.
One idea could be that the mad scientist discovers Percy's demigod powers and tries to replicate them in a lab - creating some sort of artificial half - blood. Another could be that the mad scientist is working for a Titan and is using his inventions to try and defeat Percy and his friends. Or perhaps the mad scientist has created a time - traveling device and accidentally sends Percy to a time when the gods were first born, causing all sorts of chaos.
One idea could be a quest where Percy and Artemis have to team up to rescue a group of demigods captured by a powerful new enemy. Maybe a Titan who has found a way to drain the powers of young demigods. Percy's skills in water manipulation and combat, combined with Artemis's archery and her connection to the moon, would make for an exciting adventure as they face various challenges along the way.
Well, a plot could involve Percy Jackson stumbling upon a hidden cave where cavemen are in a sort of stasis. When they wake up, they mistake Percy for a god because of his powers. Percy then has to teach them about the modern world while also learning about their primitive yet magical ways of life. Maybe there are ancient artifacts in the cave that are related to the Greek gods and Percy has to protect them from being misused.
One plot idea could be that Percy has to face Arachne in a battle of wits rather than just a physical fight. Maybe Arachne weaves illusions within her webs that Percy has to break through to reach her. Another could be a scenario where Arachne tries to use Percy to get revenge on the gods by tricking him into stealing an important artifact from Olympus. A third idea is that Percy and Arachne form an unlikely alliance when a greater threat emerges that endangers both of their existences.
A plot could involve Percy accidentally stumbling into Artemis' territory. At first, Artemis is angry but then realizes Percy has information about a threat to her hunters. So they start an adventure to stop this threat. During the journey, they learn more about each other's worlds and develop a mutual respect. Or maybe there's a spell that makes Artemis lose her powers temporarily and Percy has to protect her while she regains them.
A really interesting plot could be that Cupid, for some reason, decides to make Percy the ultimate symbol of love in the demigod world. Percy is then thrust into a role he doesn't understand, having to deal with love - sick demigods coming to him for advice. Meanwhile, he has his own relationship problems, like his feelings for Annabeth being complicated by this new status. He has to figure out how to handle Cupid's meddling and restore some normalcy to the love lives of those around him.
One idea could be Percy having to adapt his demigod skills to his new situation in a wheelchair. For example, he might have to figure out new ways to fight monsters. Maybe he uses his wheelchair as a weapon somehow, like ramming into foes or using it to block attacks. Another plot could involve his friends helping him adjust, and together they discover new powers or artifacts that are specifically useful to him in his wheelchair - bound state.
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.
Another plot could involve Percy getting a vision from Athena about a future threat to the demigod world. But the vision is so cryptic that he has to work closely with Athena to decipher it. Along the way, they build an unexpected bond, different from his usual relationships with other gods. Maybe Percy starts to see Athena not just as a powerful deity but as a mentor figure, and Athena starts to respect Percy's tenacity more than she expected.
One idea could be that the gods have lost their powers due to some ancient curse, and it's up to Percy and his friends to find a way to restore them before the apocalypse fully hits. Maybe they have to journey to the very origin of the gods' power.