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.
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.
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.
One key element could be Percy's use of his water - based powers in a unique way. Maybe he creates a huge tidal wave to disrupt Kronos' forces. Another element might be his alliances. He could team up with his friends from Camp Half - Blood, and they all use their combined skills to outwit Kronos.
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.
Annabeth Chase is likely to be one of the supporters. She is smart and strategic, and she can come up with plans to help Percy. Grover Underwood, Percy's satyr friend, might also be there. He can use his nature - related powers to help in the fight. Maybe some of the other demigods from Camp Half - Blood like Jason Grace or Piper McLean could also show up to support Percy.
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.
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.
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.
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.
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.