Who could be the main antagonists in 'Percy stays behind in Tartarus fanfic'?

One possible plot development could be Percy facing off against new and terrifying monsters that are unique to Tartarus. Maybe he discovers some long - lost secrets about the place that could change the way the demigods view Tartarus in general.

The Titans that were banished to Tartarus could be major antagonists. They might see Percy as an intruder and a threat, and try to stop him from escaping or even try to use him for their own purposes. Also, the various monstrous creatures native to Tartarus, like the Empousai or the Arai, could constantly be attacking Percy.

There could also be a group of demigods who are jealous of Percy's power due to his unique parentage. They might form an alliance against him, trying to steal his powers or at least make his life difficult. They could be led by a demigod who has a grudge against Percy or is power - hungry.

The monsters native to Tartarus could also be antagonists. These could be huge, grotesque creatures that have never seen the outside world. They might attack Percy on sight, seeing him as prey. Some of them could be powerful enough to even give Percy a hard time, especially if his powers are weakened in Tartarus.

The Titans or Giants that were banished to Tartarus could be the main antagonists. They might see Percy as a threat or an opportunity to escape and seek revenge on the Olympians.

Maybe it's the Titans who are still lurking in Tartarus and don't want Percy and Zoe to succeed in whatever mission they have. The Titans could see them as a threat to their potential future plans of rising again.

Some of the more powerful and vengeful spirits in Tartarus could be the main antagonists. These spirits could possess demigods or mortals close to Percy to get to him. They might be angry that he escaped their domain and want to drag him back. Additionally, there could be a group of rogue demigods who believe that Percy has been corrupted by Tartarus and they see it as their duty to stop him, even if it means becoming his enemies.

Perhaps there's a new villain, a powerful sorcerer who has a vendetta against Percy. The sorcerer discovers that Percy is now at high school and decides to target the school. He uses his magic to create illusions and manipulate the minds of the students and faculty, turning them against Percy. The sorcerer might also be after the secrets Percy learned in Tartarus, thinking it can give him more power.

Another character that could be involved is Nico di Angelo. Since he has some experience with the Underworld and Tartarus, he might try to find a way to communicate with Percy or even attempt a rescue mission. His powers and knowledge would play an important role in any interaction with Percy in Tartarus.

In the fanfiction, the environment of Tartarus itself could be considered an antagonist. The extreme heat, the toxic gases, and the ever - present danger of falling into bottomless pits. And on top of that, there could be some sort of demon - like creatures that are specifically created or summoned to hunt down Percy and Zoe and prevent them from achieving their goals.