Fanfiction about Kronos, the Titan of Time, can be really interesting. It often explores his power over time in unique ways. Some fanfictions might focus on his backstory, like his rise and fall among the Titans. Others could be more about his relationships with other deities or mortals in a fictional, creative context.
Time manipulation is of course a big theme. Writers in these fanfictions play with the idea of Kronos' control over time. They might create scenarios where he alters time to change the fate of the world or his own. And there's also the theme of betrayal. Kronos was betrayed by his own son, and this can be explored from different angles in fanfiction, like what led to the betrayal and how Kronos feels about it.
Hesiod was one of the first to mention Kronos in his epic works like 'Theogony'. His accounts were very important in establishing the early understanding of Kronos and the Titans in Greek mythology.
Perhaps there are some traitors from the other side. These characters, seeing Kronos' power and potential for victory, switch sides and help him in the war. They might provide valuable information about the enemy's defenses and plans.
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.
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.
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.
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.
To develop the character, start with his backstory. Since he's the son of Kronos, he might have grown up in a very different environment compared to other demigods. Maybe he was hidden away by a minor god who felt sorry for him. His past experiences of being alone and shunned because of his father would shape his personality, making him a bit of a loner at first.