Well, one possible plot could be Percy discovering new powers. Since Hecate is the goddess of magic, Percy might learn magical abilities he never knew he had. Maybe he starts to see magic in everyday things in a way he didn't before. For example, he could make inanimate objects come to life or use spells to protect himself and his friends. Another aspect could be his relationship with Hecate. She might be a strict but loving mother figure, teaching him about the deeper mysteries of the demigod world and how magic fits into it all.
In a 'Percy Jackson adopted by Hecate' fanfiction, the plot might center around Percy's identity crisis. He has always been known as Poseidon's son, but now with Hecate as his adoptive mother, he has to reconcile his old identity with this new one. He could struggle with how to use his water powers in combination with his new magical powers. Hecate might send him on a quest to retrieve a powerful magical artifact. Along the way, he meets other demigods and magical beings, some of whom become his allies and some his enemies, all while trying to figure out his place in this new magical - demigod world.
The plot could involve Percy being taken to a hidden realm by Hecate. In this realm, he is trained in magic and the secrets of the ancient world. He might encounter strange magical creatures that are loyal to Hecate. Also, Percy could face challenges within the demigod community because of his newfound connection to Hecate. Some might be jealous or suspicious of his new powers, while others might seek his help. And he could use his new magical skills to solve problems that normal demigod powers couldn't handle.
One possible plot could be Percy discovering new powers bestowed upon him by Hecate. He might have to use these powers to navigate a mysterious underworld realm filled with strange creatures. Along the way, he could meet new allies who are also under Hecate's influence.
The plot could also be about the daughter of Hecate uncovering a dark magic plot that endangers Camp Half - Blood. She initially tries to handle it on her own but realizes she needs help. Percy Jackson gets involved and they start to investigate. Along the way, they discover that the source of the problem is an ancient curse related to Hecate herself. The daughter has to come to terms with her heritage and use her powers in ways she never thought possible to break the curse and save the camp.
His relationship with Annabeth would change. She might be a bit jealous at first of Percy's new connection to Hecate. But then she would see how his new powers could be useful. They would have to learn to work together in a new way, with Percy having different abilities to bring to the table. His friendships with other demigods like Grover would also be different. Grover might be a bit in awe of Percy's new magical side. Percy would also have to form new relationships with the followers of Hecate, who might be very different from the demigods he's used to.
A plot could be that Percy is given a prophecy that involves him having to form a new kind of family unit. He decides that adopting Thalia is part of fulfilling that prophecy. But in order to fully embrace this new family, they need to go on a journey to different mythological realms. In each realm, they face different challenges that test their relationship. For example, in the Underworld, they have to deal with Hades who is not too happy about their new arrangement. This forces them to rely on each other and grow closer as they overcome these obstacles.
Well, one possibility could be that Percy, already a hero in his own right, finds himself in a situation where Apollo decides to adopt him. Maybe Percy has lost his connection to Poseidon for some reason, and Apollo sees his potential. Apollo could then train Percy in new ways of using his powers, not just related to water but also in areas like prophecy or archery, which are Apollo's domains.
One possible plot could be Percy's struggle with his new identity. Since Hera is the goddess of marriage and family, Percy might find himself in a very different family dynamic. He could be thrust into the middle of godly politics more than ever as Hera's adopted son. For example, he might have to deal with the jealousy of other gods' children who see him as having an unfair advantage.
In a 'Percy Jackson adopted by Artemis' fanfiction, perhaps Percy is exiled from Camp Half - Blood due to false accusations. Artemis, who has always been intrigued by Percy's courage, takes him in. With Artemis as his new guardian, Percy gets involved in the Hunters' battles against ancient monsters that threaten the world. He also has to deal with the jealousy of some of the other Hunters who are not happy about a male being in their midst.
One idea could be Percy seeking help from Hecate to break a powerful curse that has been placed on Camp Half - Blood. Another could be Hecate tasking Percy with a quest to retrieve a magical artifact that she needs to maintain the balance of magic in the world. Maybe Percy has to enter the realm of Hecate and face various magical trials to gain a new power.
Well, one possible plot could be Percy struggling to adapt to his new 'mother' Khione. He might have to deal with her cold and often unfeeling nature. For example, she could be trying to train him in her own ways which are very different from what he's used to at Camp Half - Blood. Maybe she wants him to use his powers in a more aggressive way to serve her own purposes.
In a 'wolf percy jackson adopted by the hunt' fanfiction, it might start with Percy being alone and injured. The wolf, which could be a magical or sentient one, leads him to the Hunt. The Hunt, which is a group of strong female hunters, may initially be hesitant to take in a male like Percy. But as they get to know him and his skills, they realize he can be an asset. Percy would then have to adapt to their rules and code, which could lead to some interesting conflicts and character development.