Well, there's a fanfic called 'Crossing Realms'. In this one, the Egyptian magic system from the Kane Chronicles and the Greek mythology elements of Percy Jackson collide. It has some really cool fight scenes where the powers of both universes are pitted against each other. The author does a great job of making the two different mythologies work together in the story.
I really like 'Alliances of the Ancients' in the world of Kane Chronicles - Percy Jackson crossover fanfics. This story focuses on how the characters from the two series form alliances to face a common threat. It delves deep into the personalities of the characters, like how Percy's quick - thinking and Carter's knowledge of Egyptian magic complement each other. It's a long and detailed fanfic that really keeps you hooked.
One idea could be that the demigods from Percy Jackson's world accidentally stumble into the realm of the Kane Chronicles. Maybe Percy, Annabeth and some of their friends are on a quest near a portal that leads to the Egyptian magical world. Once there, they meet Carter and Sadie Kane. They soon realize that there's a common enemy that is affecting both their worlds, like an ancient evil that was sealed away long ago but is now starting to break free. They have to combine their powers, the Greek magic and the Egyptian magic, to fight it off. For example, Percy's control over water could be used in creative ways in the Egyptian deserts, and the Kane's magic could help the demigods in understanding some new types of magical threats.
Maybe there could be a new threat that can only be defeated by combining the magic of the Greek demigods and the Egyptian magicians. For example, a powerful monster that is immune to the weapons of one group but vulnerable to the powers of the other. Percy and his friends would have to team up with Carter, Sadie and their crew to take it down. They would need to learn about each other's worlds and powers along the way, which could lead to some interesting character interactions.
One great 'Percy Jackson Twilight crossover fanfic' is 'Twilight of the Gods'. It combines the mythological elements from Percy Jackson with the vampire - werewolf lore of Twilight in an exciting way. The characters from both universes interact in a really interesting plot that keeps you hooked.
I really liked 'When Hunters Meet Demigods'. In this fanfic, the concept of how the hunters from Supernatural would react to the demigods in Percy Jackson's world is explored. It's full of action scenes where the skills of the hunters and the powers of the demigods are pitted against common enemies. It's a short but exciting read.
One great Percy Jackson RWBY crossover fanfic is 'Percy in Remnant'. It has an interesting plot where Percy somehow ends up in the RWBY world and has to navigate its unique challenges while still having his demigod powers. The story does a good job of blending the two universes' elements.
First, know both universes well. Read the original books thoroughly. Then, create a unique plot that can blend the two worlds in an interesting way. For example, you could have a quest that involves both Greek and Egyptian mythology elements.
Definitely Percy and Carter. Percy is used to his own brand of heroism and power from the Greek world, while Carter has been trained in the ways of Egyptian magic. They could start off being a bit competitive, each thinking their own way is better. But as they face challenges together, they would learn to respect each other's skills. For example, when they are fighting a combined Greek - Egyptian monster, Percy's quick thinking in battle and Carter's knowledge of ancient spells could complement each other.
Annabeth and Sadie would be really interesting. Annabeth is super intelligent and strategic in the Greek way, while Sadie is a powerful magician with her own brand of cleverness from the Egyptian side. They could either be rivals at first, competing over who has the better knowledge or skills, or they could quickly realize that they can achieve more by working together. They could exchange ideas about architecture (since Annabeth loves it) and magic spells, creating a unique dynamic.
Maybe there's a magical artifact that has significance in both Egyptian and Greek mythology. The characters like Percy and Carter Kane have to team up. Percy could use his water powers and Carter his magic to navigate through various challenges. They might start off distrusting each other because of their different mythological backgrounds but then realize they need to work together to stop the artifact from falling into the wrong hands.
I really like 'Kane Chronicles and Magnus Chase: A Crossover'. This fanfic is amazing as it brings together two Rick Riordan universes. It delves deep into how the different mythologies can co - exist and interact. The author does a wonderful job of creating new adventures for the characters from both series.