Percy Jackson would likely still be a main character. He has such a central role in the original series that it's hard to imagine a fanfiction without him. Another might be Annabeth Chase, as she's Percy's close companion. There could also be new characters created specifically for this fanfiction, like a mysterious ultimate life form character who becomes Percy's ally or adversary.
Percy is definitely one of the main characters. His journey in the fanfiction might involve him exploring the world of the ultimate life form. Then there's Grover, Percy's satyr friend. He could play an important role in the fanfiction as well, perhaps using his connection to nature to interact with the ultimate life forms. And of course, there could be a powerful and enigmatic ultimate life form as a main character that drives the plot forward.
One interesting concept could be new powers for Percy. Maybe he has the ability to control not just water but also other elements related to the sea, like the ability to manipulate sea creatures' minds on a deeper level. Another concept might be a new form of the ultimate life form, perhaps a hybrid of different mythological creatures that combines the strength of a centaur, the speed of a harpy, and the wisdom of a sphinx.
One of the top authors is 'SeaFan123'. Their stories always have a great flow and they really understand the Percy Jackson world. Another good one is 'DemigodWriter99'. They often come up with really creative plot ideas. And 'CampHalfBloodAuthor' is also great as they write in a way that makes you feel like you're right there at Camp Half - Blood.
Obviously, Percy Jackson himself is likely to be one of the main characters. He's the protagonist in the Percy Jackson series, so he would be central to this fanfic too. Annabeth Chase would also probably be involved as she is Percy's close friend and often by his side in adventures. Grover, Percy's satyr friend, might also be there as he's always been part of Percy's journey.
A new type of sea nymph who has the ability to change the color and texture of water. She could be from a far - off part of the ocean that Percy has never explored. Her appearance could bring new mysteries and adventures for Percy, as she might know secrets about the deep sea that are crucial to the safety of the demigod world.
Obviously, Atlas is a main character. He's often portrayed in different ways, sometimes as a more sympathetic figure trying to break free from his past, or as a more menacing antagonist still holding onto his old grudges. Percy Jackson also often shows up. His interactions with Atlas can range from confrontational to reluctantly allying with him.
Obviously, Percy Jackson himself is usually a main character. He is the one who gets involved in the devil - related situations. And then there could be new characters created specifically for the fanfiction, like a devil - like antagonist who is trying to corrupt Percy or the world around him.
The main characters are, of course, Percy Jackson and Frank. Percy is the son of Poseidon, a brave and resourceful demigod. Frank is a son of Mars in the Roman aspect, with his own set of unique powers and a shy yet determined personality. They often interact in these fanfictions, either as friends, allies in a quest, or sometimes having to overcome differences.
In this fanfiction, Percy Jackson is the key character. However, there could be new characters introduced who are related to the pets. Maybe there's a pet owner who Percy teams up with. Or perhaps there are veterinarians in the demigod world who help Percy when the pets get sick or injured. And the pets themselves, which could range from a cute little mouse with a big secret to a majestic eagle that can fly faster than the wind, would be important main characters in the story.
There could also be new characters created specifically for the fanfiction. Maybe a new demigod who has some sort of power that is related to both Percy's water powers and Juniper's nature powers. This new character could bring a fresh dynamic to the story and be either a friend or a foe to Percy and Juniper as they navigate through the plot.
Percy Jackson is the central figure for sure. The dragon is another main character, whether it's a friendly or a menacing one. There could be new characters created specifically for the fanfiction. For example, a dragon tamer from an ancient demigod lineage who has knowledge about the dragon's kind. This character could either be an ally or an antagonist to Percy. And of course, we might see some of the minor gods or goddesses make an appearance, as they often have their own interests in the affairs of demigods and magical creatures like the dragon.