In some fanfics, it could be related to Percy's powers. His powers might be growing too strong and the gods feel threatened. They fear that he could one day overthrow them or disrupt the order they have established. So, as a preventive measure, they banish him to Tartarus. Also, it could be due to his relationships. If he starts getting too close to a forbidden or dangerous entity, the gods might see this as a threat and banish him.
Well, perhaps in the fanfic, there's a prophecy that gets misinterpreted. The gods think Percy is going to cause great harm based on this wrong interpretation, so they send him to Tartarus. It could also be that there's some sort of power struggle among the gods. Percy might be caught in the middle of it, and one side decides to get rid of him by banishing him to Tartarus to tip the balance in their favor.
Well, one reason could be that he's wrongly accused of a major crime against the gods. Maybe some false evidence is planted, making the gods believe he's a threat, so they banish him. Another reason might be that he's trying to protect someone or something, and his actions are misinterpreted as going against the gods' will. For example, if he's trying to save a powerful but 'forbidden' creature, the gods might see this as a violation and send him to Tartarus.
Perhaps a prophecy misinterpretation. If a prophecy was misread and it seemed like Percy was the cause of great evil to come, the gods might take drastic action. For instance, if the prophecy spoke of a 'child of the sea' causing destruction, and they wrongly assumed it was Percy without fully understanding the context.
In a 'percy banished to tartarus fanfic', the plot could be about Percy's internal battle as well. He's been banished, which could make him feel betrayed and angry. So he not only has to deal with the physical threats in Tartarus but also his own emotions. He could question his identity and his purpose, and this self - discovery could be a major part of the story. He might start to see things from a different perspective, and this new understanding could be crucial in his journey to either escape or change his situation in Tartarus.
There are several possible reasons. Firstly, for the sake of drama. It makes for a very intense and emotional story when a beloved character like Percy dies. Secondly, it could be to explore the after - effects on the other characters. How would Annabeth cope? How would the Camp Half - Blood react? Also, it might be a way to show the unforgiving nature of Tartarus.
In some fanfictions, Percy might be banished because he goes against the traditional ways of the demigod society too much. For example, if he tries to form an alliance with a group that the other demigods consider enemies. His actions could be seen as a threat to the stability of their world, so they banish him to keep the peace.
Maybe an old and powerful monster that has long been trapped in Tartarus could be the main antagonist. It sees Percy as a threat or a source of entertainment, and it tries to stop him from finding a way out or from getting stronger.
She could be banished due to her unorthodox powers. In many fictional settings, if a character has powers that are different or not understood by the majority, they are often feared. If female Percy has some unique abilities that are considered dangerous or abnormal, the authorities or those in charge might decide to banish her to keep the peace or protect their own interests.
Annabeth might be able to save him. She's smart and resourceful, and she'd do anything to get Percy back.
First of all, Percy's resourcefulness would come into play. He would probably try to make allies among the less - hostile creatures in Tartarus. He has a way of befriending those who are often overlooked. Also, he would use his knowledge of Greek mythology. Since he knows about many of the monsters and their weaknesses from his studies, he can use this knowledge to survive. His connection to his friends, even if they are far away, might also give him the strength and motivation to keep going and find a way to escape or at least endure.
It could be due to some sort of poison or magical spell. In the Percy Jackson universe, there are all kinds of creatures and magic that could cause such a reaction. For example, if he was exposed to a slow - acting venom from a mythical beast, it might gradually make him faint.