His friends like Annabeth might come to his rescue. Annabeth is smart and resourceful, she could figure out where Percy is being held and lead a rescue mission.
There's also a chance that a new character could be introduced to save Percy. Maybe a powerful demigod from a far - off place who has heard of Percy's plight and decides to help. This new character could have unique powers that are specifically useful in dealing with Kronos and his forces.
It could be Grover. Grover has a strong sense of loyalty towards Percy. He might use his nature - related powers to track Percy down and then, with the help of some other demigods or even some unexpected allies, free Percy from Kronos' clutches.
One possibility is that Kronos captures Percy to steal his powers. Percy, being a powerful demigod, has abilities that Kronos desires for his own evil plans. While captured, Percy may discover some secrets about Kronos' past that could be used against him. He has to use his wits and any small resources he has in the prison to outsmart Kronos and break free.
Chiron could also be a key figure in trying to save Percy. As the centaur trainer at Camp Half - Blood, he has a lot of knowledge and connections. He might try to negotiate with the gods on Percy's behalf or find some loophole in the gods' actions to free Percy.
Maybe there are some original characters created by the fanfiction author. These characters could have their own unique abilities and backstories. They might be the ones who tip the scales in Percy's favor, for instance, by having a special power that weakens Kronos just before Percy makes the final blow.
Luke could also be a prominent character. Since he has a complex relationship with Kronos in the original story, in fanfiction he could play a role in either helping or hindering fem Percy's efforts against Kronos. Nico di Angelo is another possibility. His powers over the dead could be useful in a fight against Kronos, and he might team up with fem Percy for that reason.
In many fanfictions, Percy might use his water powers in a unique way. Maybe he combines his control over water with his sword fighting skills. He could create a giant water vortex to disorient Kronos and then strike with Riptide while Kronos is off - balance.
Annabeth is often a popular character. In fanfiction, she might play a crucial role in helping Percy deal with his complex identity as the son of Kronos. Grover could also be popular as he's Percy's loyal friend and could be there to support Percy through his struggles related to his new - found heritage.
Some of Kronos' minions, like the monsters he commands, could be antagonists. For instance, the dracaenae. They are always eager to prove themselves to Kronos and might see Percy as competition within Kronos' ranks. They could constantly try to undermine Percy's position and cause trouble for him.
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.
Yes, there are likely some fanfictions out there with this concept. The Percy Jackson fandom is quite large and creative, so it's possible for fans to explore such an interesting and unorthodox relationship in their stories.
One great Kronos fanfiction could be about his backstory before he turned evil. Maybe it explores his relationship with the other Titans and what led him to start the war against the Olympians.