Annabeth could be a crucial supporting character. She might use her wisdom to come up with a battle plan. For example, she could figure out the best time and place for Percy to attack Gaea based on her knowledge of ancient prophecies and Gaea's patterns.
Well, Annabeth could be added. She would be really important as she is Percy's love interest. Her intelligence and strategic mind could play a big role in dealing with Gaea. Maybe she tries to find a way to break Gaea's hold on Percy if Gaea has some sort of power over him. Another character could be Nico di Angelo. His powers over the dead might be useful in uncovering secrets about Gaea's past and weaknesses. He could also be a voice of reason for Percy when Percy is in a difficult situation with Gaea.
One possible scenario could be that Percy uses his water powers in a very unique way. Maybe he combines the power of the ocean with some sort of ancient magic he discovers to defeat Gaea. He could summon a massive tidal wave that not only physically overwhelms Gaea but also disrupts her connection to the earth.
Kakashi could be a significant supporting character. He could provide Naruto with some advice or even join the battle alongside Naruto for a while. Another possible supporting character could be Hinata. Her gentle presence and belief in Naruto could give Naruto the extra motivation he needs during the fight.
Obviously, Percy will be the main character. He is the one doing the destroying after all.
Obviously, Percy and Gaea would be the main characters. But there could also be other characters like Annabeth. She might be heartbroken at first when she hears about Percy's marriage to Gaea. And then there could be some of the other demigods like Jason or Piper who would be involved in trying to understand what's going on and maybe even stop it if they think it's a bad thing.
Another character could be Annabeth. She might try to stop Percy from taking such extreme actions, or she could be on his side if she believes the hunters are in the wrong. Grover could also be there, trying to play the peacemaker between Percy and the hunters. And then there could be some new, made - up characters in the fanfiction, like a rogue hunter who sides with Percy or an antagonist within the hunters' ranks who pushes Percy to his limits.
Gaea herself would obviously be a main antagonist. She has the power to manipulate the earth and all its forces against Percy. Her children who are fully committed to her cause could also be major antagonists. They might have powers related to the earth and be very difficult for Percy to defeat.
Well, it could be a really wild ride. Percy joining Gaea would be such a shock to his friends. They would probably think he's been brainwashed. And Percy himself might be in for a rude awakening when he sees Gaea's true intentions. She could be using him to get to other demigods, or to start a war between the gods and the demigods. He'd have to figure out a way to break free from her influence before it's too late.
The plot might involve Percy gathering ancient artifacts or allies. He could go on a quest to find a weapon that can harm Gaea on a fundamental level. Along the way, he overcomes many challenges and personal demons. When he finally faces Gaea, he combines his strength, the power of his friends, and the magic of the artifacts to completely destroy her, bringing peace to the world of the gods and demigods.
One possible plot could be Percy having to overcome some sort of magical or divine interference. Maybe he has to prove his worth to Gaea in a series of trials. Another aspect could be how the other demigods react to this union. Some might be in shock, while others might try to stop it for the greater good.