Percy could be a pirate with a wild and carefree attitude, always ready for a fight on the high seas. His powers over water would make him feared among other pirates. Annabeth, on the other hand, would be more refined as a pirate. She'd use her knowledge of architecture and engineering to improve the pirate ship. For example, she could design better defenses or more efficient storage for loot. She would also be the one to keep Percy in line when his pirate ways got a bit too reckless.
One idea could be that Percy and Annabeth are on a pirate ship, and they discover a hidden treasure map. They have to battle other pirates and sea monsters to reach the treasure. Another could be that they are pirates who are trying to free a group of captured demigods. A third idea is that they are pirates on a quest to find a magical artifact that can control the seas.
Well, perhaps the fanfic could start with Percy and Annabeth being magically transported into a world of pirates. They are initially confused but quickly realize they need to work together. Percy might be a natural at sword - fighting on the ship, while Annabeth tries to figure out the politics among the different pirate crews. They could be on a quest to find a magical artifact that the pirates believe will give them ultimate power over the seas.
The main antagonists could be other pirate crews. There might be a particularly ruthless pirate captain who wants to take over Percy and Annabeth's ship and all the treasures they might be after. This captain could be jealous of Percy's powers and see him as a threat.
In a large number of Percy and Annabeth fanfictions, they are indeed presented as soulmates. Their shared adventures, the way they understand each other without many words, and the deep loyalty they have for one another all contribute to this perception. Fanfiction authors often build on their existing relationship from the original works and enhance it to the level of soulmates. They might show it through things like Percy being able to sense Annabeth's distress from afar, or Annabeth always knowing exactly what Percy needs in difficult situations. This soulmate - like relationship makes for very engaging and heart - warming stories in the fanfiction realm.
It could be that Annabeth has a misunderstanding about Percy. She might think he's a threat to her position or status at the camp, so she bullies him to try and keep him in check.
It could be Chiron, the centaur. He's always keeping an eye on the campers and would likely be concerned if he caught them up to something. He might give them a stern talking - to and some extra chores as punishment.
Percy might be a bit flustered and embarrassed. He's protective of his relationship with Annabeth, so having Magnus walk in might make him feel like their privacy has been invaded. He could quickly try to shield Annabeth or just look really shocked.
Their shared experiences play a big role. They've been through so much together, like countless battles and adventures. Percy has seen Annabeth in tough situations and he knows how strong she is, but also how vulnerable. So he feels the need to protect her. For instance, they might have had a close call in a previous adventure where Annabeth was nearly killed, and that memory makes Percy extra vigilant.
Their relationship is likely to be complex. They are friends and comrades who have fought side by side many times. So, there's a strong bond of loyalty between them.