Well, Poseidon in Percy's body could have a hard time fitting into the mortal world. He'd be used to his own grandeur and might find Percy's normal life quite challenging. For example, dealing with school and friends in a way Percy does would be new to him. Also, the interactions between the two while in each other's bodies, like how they communicate and try to reverse the swap, can be really engaging.
In this kind of fanfiction, a possible plot point is how Percy, in Poseidon's body, reacts to the other gods. He might have to navigate political intrigue among the Olympians. Meanwhile, Poseidon in Percy's body could discover new things about Percy's relationship with his mother. He may also have to face Percy's enemies, like monsters, without his full godly powers and have to rely on Percy's skills and training.
In 'star and marco body swap fanfiction', the exploration of identity is quite fascinating. They might start to see themselves from a different perspective as they live in the other's body. There could be a plot where Star discovers how strong Marco is in his own way, and Marco realizes how much Star has to deal with regarding her magic and princess duties. This newfound understanding could change their relationship in the long run, which is an interesting aspect of the plot.
Well, one interesting plot point could be the characters trying to figure out how to reverse the body swap while still maintaining their normal lives. For example, if Harry and Hermione swapped bodies, Hermione in Harry's body would have to deal with Harry's fame and the challenges that come with it, like facing Voldemort. Another point could be the relationships that change. Friends might not recognize the 'new' person in the body, leading to misunderstandings and new friendships forming.
Well, Percy has a sense of humor even in tough situations. When he's in Poseidon's body, this could come out in unexpected ways among the other gods. He might crack jokes during serious godly meetings. Poseidon, who is usually solemn, in Percy's body could slowly start to understand Percy's more light - hearted approach to life. And Percy, in Poseidon's body, would have to deal with Poseidon's more complex and sometimes brooding personality when interacting with other deities.
One plot idea could be Percy having to go on a quest specifically guided by Poseidon's hidden messages in the sea currents. He has to decipher these messages to find a lost artifact that can save the underwater kingdom from a new, mysterious threat.
One possible plot point could be that Percy's resemblance to Poseidon causes confusion among the other characters. They might mistake him for Poseidon at first glance, leading to some comical or tense situations.
Another plot point is how they interact with the other characters. Bellatrix in Harry's body might have to fool his friends, and Harry in Bellatrix's body could try to manipulate the Death Eaters. This can lead to some really intense and cleverly written scenes, like when Harry tries to subtly change the Death Eaters' plans while in Bellatrix's guise.
One interesting plot point could be how they adjust to each other's abilities. For example, Ash suddenly having to deal with May's knowledge of Pokémon contests, and May having to handle Ash's battling skills. Another could be the reactions of their friends and Pokémon. Their Pokémon might be confused by the sudden change in their trainers' behavior.
One idea could be Percy having to face a new threat underwater that only Poseidon can help him understand. Maybe a lost civilization that Poseidon once had a connection with is now causing trouble. Another could be Percy going on a quest to find a powerful artifact that was once Poseidon's but has been stolen, and Poseidon gives him special powers or guidance along the way.
In this type of fanfiction, a possible plot is that Poseidon raises Percy away from Camp Half - Blood to protect him from the prophecy. As Percy grows up, he becomes more in tune with his water powers. He could then have adventures in the ocean, like finding lost civilizations or facing off against sea monsters that Poseidon sends his way to test him.
One interesting plot point is the characters having to adapt to new abilities. For instance, if Naruto swaps with Kakashi, he has to figure out how to use Sharingan properly. Another is the way relationships change. If Sakura swaps with Ino, they might understand each other's insecurities better. Also, the comical misunderstandings that can occur, like when a character doesn't know the habits of the body they're in.