Maybe an ancient god or goddess who has been forgotten by most but still holds great power in magic. This deity could see potential in Percy and choose to teach him magic as a way to bring back some balance in the world. It could be a goddess of magic who was once a part of the pantheon but has since been overshadowed.
Percy is the main character. There could be a powerful and mysterious mage who serves as a sort of antagonist at first. This mage tests Percy's skills and knowledge of magic. But as the story progresses, they might end up having a more complex relationship, like a reluctant alliance when they face a common, greater threat.
Well, perhaps Percy discovers a hidden magic within himself that he didn't know he had. Maybe he starts off struggling with basic spells and then gradually masters more complex ones. For example, he could be trying to make objects levitate at first and later on be able to conjure powerful shields.
Well, maybe Percy stumbles upon a hidden magical realm where he meets an old wizard who decides to teach him magic. He could learn spells to control water in new and extraordinary ways, like turning it into different shapes or using it to communicate over long distances.
One possible scenario in this fanfiction could be that Naruto, being banished from his village, stumbles upon a magical realm. There, he might meet a mentor who teaches him magic. This could lead to him developing new powers and a whole new identity, different from the ninja he once was. It could also open up opportunities for crossovers with other magical universes in the fanfiction world.
Perhaps it's a magical crystal that enhances his ability to communicate with magical creatures. This would be quite unique as it would give him an edge in dealing with things like thestrals or unicorns, and open up new storylines in the fanfiction. Harry could use this crystal to understand their needs and gain their help in various situations.
In a Naruto learns God Slayer magic fanfiction, it could be really exciting. Naruto's already powerful ninja skills combined with God Slayer magic would make him an even more formidable force. He could use the magic in battles against tough enemies like Akatsuki members. Maybe he'd learn it from a mysterious character who travels between different dimensions, and this new power would give him an edge in protecting the Hidden Leaf Village.
Naruto could use his newfound magic to make alliances with other magical beings. This would expand his influence and power base. He could then use these alliances to either seek revenge on those who wronged him or to protect the world from greater threats that the ninja world alone couldn't handle. In this fanfiction, the possibilities are endless as magic adds a whole new dimension to his character.
Hermione could be a strong ally. She's smart and could help Harry research more about battle magic. Ron too, with his loyalty and courage, would be by Harry's side.
Obviously, Harry Potter is the main character as the title implies he is the one learning magic early. But there could also be Hermione and Ron. Hermione might be intrigued by Harry's newfound knowledge and Ron could be both a bit jealous and in awe of Harry's early magical abilities.