One interesting plot twist could be that the daughter of Nyx has a hidden power that is the key to saving Olympus from a new, unknown threat. Maybe she can control time in a way that no one expected, which throws the whole dynamic between the gods and demigods into chaos.
Romantic relationships can also be a part of it. In some fanfictions, the daughter of Nyx might develop feelings for Percy over time. This could be a slow - burning romance where they first become comrades in arms, and then as they understand each other better, deeper feelings start to emerge. Their relationship could be complicated by the fact that she is from a different and more mysterious lineage compared to Percy, which adds an extra layer of intrigue and tension.
One interesting plot twist could be that Percy discovers he has a long - lost sibling within the family. Maybe a half - brother or sister from a different godly encounter that his parents had in the past. This would change the family dynamics completely and add a new layer of relationships for Percy to navigate.
One idea could be Percy having to face a new type of monster that is related to Nyx's powers. For example, a shadow - creature that can only be defeated by using the unique abilities he inherits from being the son of Nyx.
A plot twist could be that Percy has a connection to the primordial forces that even the Titans and the Olympians are afraid of. His link to Nyx and Tartarus means he can access parts of the universe that are normally off - limits. For instance, he might be able to open portals to the darkest corners of Tartarus, which could either be a great advantage or a huge danger. Also, he could have the power to call upon the creatures of the night created by Nyx, and these creatures could be either his allies or a threat to the existing order of the demigod world, depending on how Percy chooses to use his powers.
Perhaps Percy discovers a prophecy related to his birth. It could state that he is the key to either saving or destroying the world. This would create a lot of internal conflict for him. On one hand, he has his friends and the people he cares about in the mortal world. On the other hand, his powers and his role according to the prophecy could force him to make some very difficult choices.
In some fanfictions, a cool plot twist is that the daughter of Zeus has a power that is only activated when she is in great danger. So, in a battle against a powerful enemy, she suddenly reveals this new power that completely turns the tables. It could be something like the ability to create duplicates of herself, confusing the enemy. Another plot twist could be that she has a hidden bond with a certain weapon, like a sword that has its own consciousness. The sword might choose her as its wielder, and together they have powers that are far greater than expected. And there could be a plot twist where she discovers that Zeus has been keeping a big secret from her about her mother, and this secret changes her whole view of herself and her place in the world of demigods.
One idea could be Percy's struggle with his new identity as Nyx's adopted son. He might face discrimination from some of the other demigods who are suspicious of his new connection. Another plot could involve Percy learning new powers from Nyx that set him apart in battles against monsters. He could also have to deal with Nyx's enemies who target him because of his relation to her.
In some fanfictions, a really cool plot twist could be that Percy's Hela - given powers are slowly corrupting him. He starts to see the world in a different, darker way. His friends notice the change in him but don't know the cause at first. As he struggles with this corruption, he has to find a way to either embrace it and use it for good in a new way, or find a way to get rid of it. Also, imagine if Percy discovers that he has a half - brother or sister from Hela's side in the Norse world, and this new relative has a completely different view on life and power, which causes more drama and conflict for Percy.
One interesting plot twist could be that the Minotaur is actually a misunderstood creature under a curse. In some fanfictions, it might be revealed that he was once a heroic figure before being transformed. Another twist could be Percy having a secret power that he discovers while fighting the Minotaur that changes the whole dynamic of their encounter. For example, he might be able to communicate with the Minotaur's mind and find out its true motives.
A really cool plot twist might be that the reincarnated character realizes they are not just reincarnated into the Percy Jackson world randomly. They are part of a prophecy that was long forgotten. Their actions in this new life will either save or destroy the world of demigods. This would add a layer of high stakes and mystery to the fanfiction.