One idea could be Percy having strange, prophetic dreams about Gaea that lead him on a quest to understand her true nature before she fully awakens. Maybe he discovers an ancient bond between them that was long forgotten. Another could be Gaea trying to tempt Percy to join her side by offering him power and the ability to reshape the world in a way he might think is better. For example, she could show him a vision of a perfect world without the constant threat of monsters, but with a hidden, dark price.
One idea could be that Percy has a dream where Gaea is trying to corrupt the power of a magical lemon tree. The lemon tree has the ability to heal demigods, but Gaea wants to use it to create chaos. Percy, with his friends, has to protect the tree. Maybe the lemons from the tree can also be used as weapons against Gaea's minions, like when thrown, they release a burst of purifying energy.
One idea could be Percy having to face challenges in a world where Gaea has more direct control over the elements. For example, the earth itself could be constantly shifting and changing, creating new terrains and obstacles for him to overcome. Another could be Percy forming an unlikely alliance with some of Gaea's other children who are also having second thoughts about their mother's destructive plans.
Perhaps the Daughter of Gaea is sent on a mission by Gaea to infiltrate Camp Half - Blood. But instead of causing harm, she falls in love with the sense of community there. She starts to secretly help the campers prepare for Gaea's attacks. She could use her connection to the earth, which is different from the demigods' but still useful, like sensing when Gaea is about to send her minions.
One plot idea could be Gaea's redemption. In the original series, she was a major villain, but in a fanfic, she could be given a chance at redemption. Maybe Percy and his friends discover that Gaea was being controlled by a more powerful and malevolent force all along, and they have to work with her to defeat this greater evil.
A really interesting plot could involve Percy being in a situation where he has to use the powers he inherited from Gaea to save the world from a new and greater threat. However, the other demigods don't trust him at first. So he has to not only fight the external threat but also earn the trust of his comrades. He might discover ancient secrets about Gaea that could either doom or save the world, and he has to make a difficult choice based on that knowledge.
One idea could be Percy having to choose between the powers of Kronos and Gaea. Another could be Percy teaming up with some unexpected allies from the realms of Kronos and Gaea to fight a new common enemy. Maybe Percy discovers a hidden prophecy that involves his lineage as the son of Kronos and Gaea and has to fulfill it to save the world.
Well, a possible plot could be Percy being sent on a quest by Gaea. But instead of following her orders blindly, he uses the quest to gather information about her weaknesses. He could form an unlikely alliance with some minor gods who also oppose Gaea. As for his relationship with his old friends, they would be in shock and some might even try to 'rescue' him from Gaea's influence, leading to some tense and emotional encounters.
In this fanfiction, there could be a prophecy about a lemon that will either save or doom the world in the face of Gaea's threat. Percy Jackson is tasked with finding this lemon. Along the way, he meets various characters who either help or hinder his quest. When he finally finds the lemon, he has to make a difficult choice. If he gives the lemon to Gaea, she might spare some of his friends but would gain enough power to cause great destruction. If he destroys the lemon, he risks angering Gaea and starting a full - scale war. So, he has to find a third option that no one has thought of before.
One plot idea could be Percy getting involved in a quest that somehow crosses Artemis' path in a way that challenges their relationship. Maybe a new threat emerges that only their combined skills can defeat, and they have to learn to trust each other despite their differences.
One idea could be that Percy and Blackjack Lemon go on a quest together to find a lost magical artifact. Along the way, they face various challenges like tricky mazes and mythical beasts.