Annabeth is also often a prominent character in such fanfictions. As a daughter of Athena, she can act as a bridge between Percy and Athena. Her own skills and relationship with Percy add depth to the stories.
One popular original character is a new demigod named Lyra. She has the power to control the elements of air and is often depicted as a fierce fighter. Another is a centaur named Orion who is a bit of a rebel. He doesn't follow the traditional centaur ways and often helps the demigods in unexpected ways. And then there's a nymph called Iris who has the ability to create illusions and is a bit of a trickster, which makes her really interesting in the fanfiction world.
Definitely Harry Potter and Percy Jackson themselves. They are the main characters of their respective series, so it's natural for them to be popular in crossovers. Hermione from Harry Potter is also quite popular as she can bring her intelligence and magic skills to the crossover scenarios.
Percy himself is obviously very popular. After all, it's his series. Annabeth is also a fan favorite, as her intelligence and strong will make for interesting storylines. Nico di Angelo is quite popular too, especially when his powers and his somewhat dark nature are explored in fanfiction.
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.
Annabeth Chase is also a fan favorite. Her intelligence and strong will make her a great character to explore in fanfiction. Writers might focus on her architectural projects in the context of the demigod world, or her relationship with Percy from different angles.
Percy is definitely one of the most popular. He's the main character in the original series, so fans love to see more of his adventures in fanfiction. Annabeth is also very popular. Her intelligence and strong will make her a great character to explore further. Another popular one is Nico. His dark and mysterious nature gives a lot of room for fanfiction writers to create interesting stories around him.
Percy himself is often very popular in fanfiction. Since he is the main character in the original series, fans love to explore different scenarios and character developments for him.
Percy Jackson himself is often very popular. Fans love to see how he would handle the situations in the SG1 universe. His humor and his ability to think on his feet make him a great character to write about in this crossover.
Percy himself is of course very popular. His heroic deeds and his journey from a somewhat naive demigod to a powerful warrior are always interesting to explore in fanfiction.
Kronos is also a popular character. His menacing presence and his complex backstory attract a lot of writers. Writers like to explore his motives for rebelling against the Olympians and what made him turn into such a villain.