Well, in fanfiction, the idea of Percy being possessive of Nico can be explored in many ways. It could be a sign of his insecurity. Perhaps Percy has lost important people in his life before and is afraid of losing Nico too. So, he becomes possessive as a way to keep Nico close. It can also be a way to show his evolving character. If the fanfiction is set in a world where there are threats, Percy's possessiveness might be his way of ensuring Nico's safety, like he doesn't trust others to protect Nico as well as he can.
It could be because of the potential for a romantic relationship in fanfiction. Some fans like to explore the idea of Nico having romantic feelings for Percy. In that case, possessiveness might be a natural part of showing his intense emotions. He wants Percy all to himself, not sharing him with others, especially when there are other characters who might also be interested in Percy.
It could mean that in the fanfiction, Zoe shows a strong sense of ownership over Percy. Maybe she doesn't like others getting too close to him or she always wants to be the one by his side. It might also imply that she is overly protective and territorial when it comes to Percy in the context of that particular fan - created story.
In fanfiction, Nico might be possessive by being overly protective of Percy. He could jump in to defend Percy even when Percy doesn't really need defending. For instance, in a situation where Percy is just having a friendly argument with someone, Nico might step in and be very aggressive towards the other person. Also, he might try to control who Percy interacts with. If there's a new demigod in the camp, Nico might try to keep Percy away from them.
If 'fe' is a person, it might imply that they consider Naruto fanfiction as something that belongs to them in a way. They could be possessive in terms of the creative control they feel they have over the Naruto fanfiction they are involved with. For example, they might have a unique interpretation of the Naruto universe in their fanfictions and don't want others to change or misuse it.
It could mean that in the fanfiction, Jackson shows a strong sense of ownership or jealousy regarding Stiles. Maybe he doesn't like others getting too close to Stiles and acts in a protective, albeit possessive, way.
In some fanfictions, their relationship might develop because of a common enemy. The threat of this enemy forces them to put aside any differences and work together closely. As they do this, they start to see the good in each other. Nico might see Percy's leadership skills, and Percy might see Nico's hidden strength and loyalty. They gradually become closer friends or even something more, depending on the nature of the fanfiction.
Percy could also become angry. He values his freedom and his relationships with his friends and family. Hades' possessiveness is a threat to all of that. So he might stand up to Hades, even if it's a risky move. He'll tell Hades that he won't be controlled or owned. He'll fight back using his powers and his wits. He might also seek help from other gods or his demigod friends who have had experiences with Hades.
In the fanfiction, Percy might use his demigod senses. Since he has been in the casino before, he knows the layout and the tricks it plays. He could be searching for any signs of Nico's presence, like his unique demigod aura or any items that Nico might have left behind as he moved through the casino.
The camp leaders might betray them. If there is a power struggle within the camp, and Percy and Nico are seen as threats to the current leadership's power, the leaders could set them up. They could make it look like Percy and Nico are breaking camp rules or endangering the other campers, which would lead to the rest of the camp turning against them.
In the fanfiction, Percy's possessiveness might also be demonstrated by his need to be included in all of Annabeth's plans. He may feel left out or threatened if she starts making plans with other people without him. He wants to be a part of everything she does, almost like he owns a part of her time and attention.