An interesting plot could be that the OC is a being of chaos who has the power to create portals to different realms. Percy and the OC meet when Percy accidentally stumbles into one of these portals. They then embark on a journey through various realms, some of which are completely uncharted by the demigod world. Along the way, they encounter strange creatures and face challenges that test their relationship. Another plot idea is that the OC is tasked by Chaos to teach Percy a new form of combat that is based on chaos energy. This would lead to some really cool training scenes and also a deeper bond between them. And, the OC could have a secret mission from Chaos that involves Percy, and as Percy gradually uncovers this mission, it adds a layer of intrigue to their relationship.
One plot idea could be Percy being sent on a secret mission by the Chaos forces to infiltrate an enemy stronghold. He uses his skills and wits to gather intelligence without being detected.
A possible plot for 'Percy is a Son of Chaos' fanfiction could be Percy being sent on a mission by Chaos itself. This mission could be to restore balance in a part of the universe that has been thrown into chaos (ironically) by some dark force. Along the way, he teams up with some unlikely allies, some of whom are also children of primordial entities. They all have different motives and powers, and Percy has to learn to work with them while also coming to terms with his own identity as a son of Chaos.
One idea could be that Percy has unique powers given to him by Chaos. For example, he might be able to control the very fabric of the universe in small ways. Maybe he can manipulate time on a very limited scale, like slowing it down during a fight to gain an advantage.
One idea could be Percy facing a new chaos - themed villain who can manipulate time in a disorderly way. Percy has to find a way to break the time - loops the villain creates.
One idea could be that Percy and Calypso find themselves in a strange new world within the chaos, where the rules of magic are all jumbled. They have to rely on each other's unique abilities to survive. For example, Percy's water - controlling skills and Calypso's nature - based magic might combine in unexpected ways to fend off the chaotic creatures they encounter.
One idea could be that Percy discovers a new power related to chaos while on a quest with Artemis. This power could be the ability to manipulate time in small bursts, which helps them escape a dangerous trap set by an ancient monster.
One idea could be Percy using his skills in a chaotic new world filled with strange mythical creatures that no one has ever seen before. He has to navigate through this chaos and find a way to bring order to this new part of the mythical realm.
One idea could be that Percy discovers a hidden connection to Chaos while on a quest. Maybe he stumbles upon an ancient artifact that has the power of Chaos within it, and it starts to change him in unexpected ways. For example, he might gain new powers that are related to the primordial chaos, like the ability to manipulate energy in a more chaotic and unpredictable form.
One idea could be Percy facing a new type of monster that is immune to water. This would really challenge his typical combat style. Another could be Percy having to team up with an old enemy to defeat a greater threat that endangers both the mortal and demigod worlds. Maybe he has to journey to a completely unknown realm within the Chaos to retrieve a powerful artifact that is the key to saving his friends.
One plot idea could be Percy's journey in the chaos realm. He could discover new powers and face challenges that are unique to that realm. For example, he might have to deal with primordial entities that test his strength and wisdom.