His friends from Camp Half - Blood, like Annabeth, Grover, and Tyson, could be the potential saviors. They have always been by his side and would do anything to rescue him.
The gods themselves might step in as saviors. Although they have a complicated relationship with Percy, they know that if Kronos succeeds in torturing and possibly turning Percy, it would be a huge threat to them. So Zeus, Poseidon, or Athena could send their champions or even come themselves to save Percy.
Well, perhaps in the fanfiction, Percy is tortured by Kronos in a way that involves his demigod powers being slowly drained. This would make him feel weak and vulnerable, which is a huge contrast to his usual strong self. His torture could also be a way for Kronos to try and break his spirit so that he can turn Percy to his side. Meanwhile, the gods might be debating whether or not to interfere, adding another layer of conflict to the story.
It could be a group of rogue demigods who are jealous of Percy's status and power. They might think that by kidnapping and torturing him, they can gain some of his abilities or just to prove that they are stronger.
The other Titans could be main antagonists. For example, Hyperion who is known for his great strength and his desire for destruction. He might not fully trust Percy and constantly try to undermine him in Kronos' eyes. Another could be Atlas, who is already a major foe in the Percy Jackson series. He might see Percy as a threat to his own plans within Kronos' regime.
There's also the possibility that a new character could be Percy's savior. Maybe a powerful and mysterious demigod who has been hiding their powers all this time. This character could have some special connection to Tartarus or a unique ability that allows them to enter the realm without being immediately overpowered. They could be drawn to Percy's plight and decide to risk everything to save him.
One way for Kronos to win in Percy Jackson fanfiction is by spreading more chaos and discord. If he could make the demigods lose faith in the gods and each other, his job would be much easier. He could also try to find a way to use the prophecies to his advantage. Maybe he could twist the words of the prophecies to make the demigods make wrong decisions. And if he could somehow break the connection between the demigods and their godly parents, the demigods would be weaker and he could overpower them.
Well, the main antagonists could be a group of rogue demigods who have formed a cult around Kronos. They believe that Percy, as the heir of Kronos, should lead them in overthrowing the current order of the demigod world. But Percy doesn't want any part of it, so they become his enemies. Another possible antagonist could be an ancient being that was once in league with Kronos and now sees Percy as a means to resurrect Kronos or continue his dark legacy. This being would stop at nothing to force Percy to embrace his role as the heir.
It could be the Titans who see Percy as a threat. Since he is the son of Kronos, they might want to either use him for their own purposes or eliminate him to prevent any interference in their plans.
Perhaps an older teacher or coach who has always had an eye on Kuroko's potential could step in as a savior. They could see the signs of bullying and use their authority to punish the bullies and provide support and guidance to Kuroko, helping him to grow stronger both on and off the court.
Hermione could be a potential savior. She's smart and resourceful. She might figure out where Lockhart has taken Harry by using her vast knowledge of magic and Hogwarts' secrets.
In fanfiction, Kronos's role is not just limited to being a villain. Sometimes, he can be a catalyst for character development among the demigods. His actions force the heroes to become stronger, both physically and mentally. For instance, his threat might make Percy Jackson more determined to master his powers. Also, Kronos can be used to introduce new plot elements, like a new weapon or a magical item that has the power to stop him.