Well, Percy might endure it through his natural demigod abilities. His connection to the water could potentially be a source of comfort or even a way to resist Kronos' power to some extent. Maybe he can draw strength from the water element around him, even in the midst of torture. Also, his combat skills might help him brace himself mentally, as he's used to facing tough situations in battles.
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.
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.
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.
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 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.
It's possible that the author of the fanfiction wanted to show Percy's growth and development in a more extreme way. So they wrote that Percy had an in - depth understanding of Kronos' weaknesses. He could then use this knowledge to quickly and easily take down Kronos. For example, he might know that a certain spell or attack would be particularly effective against Kronos, and he just exploited that weakness without hesitation.