First, you need to study the lore of all three universes. Know the powers, the characters' personalities, and the important events in Naruto, the story of Kaguya in Naruto, and the world of Percy Jackson. For example, Naruto is known for his never - give - up attitude and his powerful jutsus. Kaguya has god - like powers. Percy Jackson is a demigod with water - related powers. Understanding these is crucial.
In this fanfiction, perhaps Gaea discovers a way to use the chakra in Naruto's world to strengthen her own power. She sends her minions to capture ninja who are strong in chakra. Percy Jackson, who has a connection to the spirit world, senses this disturbance and travels to Naruto's world. Naruto and Percy meet and realize they have to work together. They gather allies from both worlds, like Naruto's friends from Konoha and Percy's demigod friends, and fight against Gaea and her forces.
If Naruto uses his Rasengan, which is a concentrated form of chakra, and Percy uses his water manipulation, they could potentially combine the two. Percy could shape the water into a sphere and Naruto could infuse it with his chakra. This combined attack would be extremely powerful. Also, Percy's ability to breathe underwater could be useful if Naruto ever gets into a situation where he needs to be underwater for a long time. Naruto's shadow clone jutsu could also be used to create distractions while Percy attacks with his sword and water powers.
One main theme is the clash and融合 of different cultures. Naruto comes from a world of ninjas with its own set of values and powers, while Percy Jackson's world is centered around Greek mythology. When they interact, especially with Zoe in the mix, there's a lot of cultural exchange and adaptation.
A really interesting plot could be that there is a tournament where demigods and shinobi compete. Naruto and Percy are the representatives of their respective groups. Along the way, they learn about each other's cultures and powers. They also discover that there are some dark forces trying to manipulate the tournament for their own evil purposes. So, they have to put aside their differences and work together to expose and defeat these forces.
One possible storyline could be a crossover where Naruto's world collides with that of Percy Jackson and Hera somehow gets involved. Maybe Naruto is transported to the Percy Jackson universe and has to deal with Hera's schemes while also trying to find a way back home. Another could be that Percy and Naruto team up to face a threat that Hera has foreseen, and they must learn to combine their powers and skills. For example, Naruto's ninjutsu and Percy's demigod abilities working together to defeat a powerful monster.
A plot idea could be that the gods in Percy Jackson's world notice the unique power of chakra in Naruto's world and decide to send Percy and his friends to investigate. Along the way, they meet Naruto and his team. At first, there are misunderstandings and small conflicts due to their different cultures and ways of fighting. But as they get to know each other, they realize they need to work together to stop an ancient evil that is trying to use the power of chakra for its own malicious purposes.
The plot could start with a strange rift opening between the Naruto universe and the Percy Jackson universe. Naruto, with the Juubi's power inside him, gets sucked into the Percy Jackson world. At first, there's a lot of confusion. The demigods are on guard, thinking Naruto is a new kind of threat. But as they start to communicate, they realize they have a common enemy in the form of a powerful being that wants to take advantage of the chaos caused by the rift. So, they team up to fight this enemy.
There's also 'Percy and His Harem of Allies'. In this fanfiction, it combines action and the development of Percy's relationships with his harem. The author does a great job of writing the characters' interactions and how Percy copes with having multiple close relationships. It's a really exciting read.
A really good 'Percy Jackson x Clarisse Fanfiction' is 'When Percy and Clarisse Train Together'. In this one, they are forced to train together and through the process, they discover new things about each other. They start to respect each other more and it's a great read for those who like character - development - focused stories.