One idea could be that the forgotten one has a special power that is the key to saving the world from a new, unknown threat. Another could be that they are actually a long - lost relative of Percy's and their connection reveals hidden secrets about the demigod world. Maybe the forgotten one was sent away on purpose by an enemy long ago and now they're back for revenge.
One idea could be exploring the backstory of the forgotten warrior more in - depth. Maybe they were once a great hero in a forgotten era of the Percy Jackson universe and got lost in time somehow. Another could be that the forgotten warrior has a special power that is now needed to defeat a new, emerging threat. They could be a key to unlocking an ancient prophecy that no one has understood until now.
Maybe in the fanfiction, Percy stumbles upon a forgotten legend about a magical artifact that has the ability to rewrite the fates of demigods. The catch is that it's hidden in a realm that is slowly being consumed by chaos. Percy, along with his friends, must navigate this dangerous realm filled with strange creatures and illusions to find the artifact before it falls into the wrong hands. They'll also have to deal with the fact that the gods are not too keen on this artifact being found as it could disrupt their carefully crafted plans for the demigods.
In 'percy jackson forgotten primordial fanfiction', there could be the idea of Percy having to deal with primordial forces that were previously unknown. This could lead to new alliances and challenges. Maybe he has to find a way to communicate with these forgotten entities, which would be a whole new aspect compared to his usual battles with known monsters and gods.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be that Percy and Hermione meet during a magical event that crosses over the Greek mythology world and the wizarding world of Harry Potter. They team up to solve a mystery that involves both magic and ancient Greek curses.
One idea could be Percy having to team up with an Amazonian princess to rescue a group of half - bloods kidnapped by a new monster. They could face challenges like navigating through the Amazon jungle filled with magical traps.
One idea could be a story where Percy has to team up with a monster that has been wrongly accused. Maybe a centaur is framed for stealing a powerful artifact from Camp Half - Blood. Percy, being the hero he is, decides to help the centaur clear its name and in the process discovers a new threat to the demigod world that involves an ancient monster alliance.
How about a crossover with the Star Wars universe? Percy could be on a strange planet that has a connection to water in a way similar to the Force. He might meet Jedi and Sith and get caught in their power struggles. His ability to control water could be seen as a strange new 'power' in the Star Wars world. Another interesting plot would be a crossover with the Percy Jackson universe and the His Dark Materials series. The daemons could interact with the Greek gods' animal forms, and Percy would have to deal with the complex moral and political issues in both worlds.
Maybe Katara gets transported to Camp Half - Blood. She initially struggles to fit in but then she realizes she can use her water - bending skills in new ways with the help of Percy's understanding of water - related powers. They could then go on a quest together to find a way to send Katara back home, all while forming a strong friendship and learning from each other's cultures.
One idea could be Percy using his gaming skills to outwit monsters in the real world of the Percy Jackson universe. For example, he might use strategies from strategy games to plan attacks against a horde of mythical beasts. Another could be Percy getting trapped in a virtual world that has elements of both the gaming world and the Percy Jackson mythos, and he has to find his way out by solving puzzles based on Greek mythology.