One plot twist could be that Percy discovers he's not actually Amphirite's biological brother. Maybe there was some kind of mix - up or a hidden secret about his origin. This would completely change his relationship with Amphirite and his place in the sea - world.
Perhaps Percy finds out that Amphirite has been using him all along to achieve her own goals. For instance, she might have been using him to gain power over a certain part of the ocean. This revelation would shatter Percy's trust in her and lead to a whole new set of conflicts and challenges for him to face.
Well, it could be about Percy's adventures in the world related to Amphirite. Maybe he has to prove himself in a world full of sea - related challenges since Amphirite is a sea - goddess. He might be on a quest to find a lost treasure that has some connection to his sister.
Perhaps a plot twist could involve Dionysus having a secret reason for raising Percy. It might turn out that Percy is part of some grand prophecy that only Dionysus knows about, and he's been grooming Percy for a specific task that will change the fate of the gods and demigods alike. This could lead to Percy having to make some really tough choices between his loyalty to Dionysus and his friends at Camp Half - Blood.
In this fanfiction, a great plot twist could be related to Percy's origin. What if Percy wasn't really born in the normal way as a god's offspring? He could be a product of some ancient magic that Zeus unknowingly participated in. This revelation could shake the very foundation of the relationship between Percy and Zeus. Also, Percy might discover a hidden side of Zeus' past that Zeus has been trying to keep secret. This knowledge could put Percy in a dangerous position as he decides what to do with this information, whether to expose Zeus or keep it to himself for the sake of their relationship.
Perhaps the plot twist is that Shisui faked his death not just to protect the village in the general sense, but specifically to keep Naruto safe. He knew of Naruto's importance as the Jinchuriki of the Nine - Tails and his relation to Naruto as a brother. So, he went into hiding and has been secretly guiding Naruto from the shadows all along. This would add a whole new layer to Naruto's journey and the events that have unfolded in the series so far.
Perhaps a plot twist could be that Draco is under the influence of a dark spell when he kidnaps Hermione, and as she tries to break the spell, she uncovers a conspiracy within the wizarding world. Or it could be that the kidnapping is a ruse set up by Hermione herself to infiltrate the Slytherin group, but Draco doesn't know it and things spiral out of control.
One possible plot twist could be that the twin brother has different magical abilities. For example, while Harry is known for his proficiency in Defense Against the Dark Arts, his twin could be a natural at Transfiguration. This would create an interesting dynamic as they could learn from each other in different ways. Another plot twist might be that the twin brother is initially hidden away for some mysterious reason, perhaps related to a prophecy that involves both of them. When he finally appears, it throws the wizarding world into chaos as everyone tries to figure out what his role is. And a third plot twist could be that the twin has a connection to Voldemort that Harry doesn't. Maybe he was unknowingly marked by Voldemort in a different way, leading to a race against time to figure out how to break that connection and save him.
One possible plot twist could be that Percy is initially oblivious to Jason's feelings. Then, just when Jason is about to give up, Percy discovers his own hidden feelings for Jason. Another twist could be that there's some external force, like a god or a prophecy, that tries to keep them apart. Or perhaps Jason discovers that Percy has a pre - existing relationship that he didn't know about, which complicates his crush.
Perhaps the monster is from a different pantheon and is raising Percy to bridge the gap between two different mythologies. Percy then has to deal with the cultural shock and the politics of two very different mythological worlds while being raised by this strange being.
One plot twist could be that their real parents are not who they thought. Maybe the gods had some grand plan and hid their true parentage. Another could be that they have some special power that only activates when they're together as siblings. For example, they could have the power to open a portal to a lost world. Also, a plot twist could be that one of them is actually in danger because of their new - found sibling relationship, and the other has to go on a dangerous quest to save them.
One possible plot twist could be that Percy is already in love with someone else, and Rachel's flirting makes things really complicated. He might be torn between his feelings for the other person and the new attention from Rachel.