Maybe a new character that combines the worst traits of Naruto's enemies and the threats in the Kamen Rider world. For example, a being that can use ninjutsu like the Akatsuki members and also has the ability to create and control the monsters that the Kamen Riders usually fight. This new villain could be after a power source that exists in both worlds, forcing Naruto and the Kamen Riders to join forces to stop it.
It could be Orochimaru from the Naruto universe. Imagine he finds a way to cross over to the Kamen Rider world. He would be attracted by the unique powers there and want to use them for his own evil experiments. His ability to manipulate and deceive would make him a formidable villain against both Naruto and the Kamen Riders.
One possible plot could be that Naruto somehow gets transported to the Kamen Rider universe. He might initially be seen as a threat due to his powerful ninja skills. The Kamen Riders could try to stop him, thinking he's a new kind of monster. But as the story progresses, they realize he's not evil and they team up to fight a common enemy that threatens both their worlds.
Well, it could be about a character from Kamen Rider Kiva getting transported to the Naruto universe. Maybe the Kiva character has to learn chakra control and ninjutsu while also trying to find a way back to his own world. He could team up with Naruto and his friends to fight common enemies like the Akatsuki who might be interested in the Kiva powers.
There were novels similar to " Masked Rider: Destroyer of the Other World " 1:" Daily Entertainment: A Glimpse of Light and Shadow." Author: Xi Xi Yan Qing 2: Fairy, Your Character Set Has Been Changed by Me, Author: Old Man Dong 3." Longevity Begins from the Forbidden Technique." Author: Super Little Erha The following is a detailed introduction of these novels: 1." Japanese Entertainment: A Glimpse of Light ": Come to Yuewen's website to read more of my works! 2:" Fairy, I've changed your character setting ":" Fairy, I've changed your character setting." "It's true.“ 3." Longevity begins with the extraction of forbidden techniques ": Reincarnated into a high-level martial arts world, Chen Xuan activates the forbidden technique system and obtains exemption from the price of the forbidden technique. Faced with the cruel situation, he had to extract forbidden techniques and open the path of crushing forbidden techniques! Permanently forbidden technique, Ten Times Longevity Burning Saber Technique. The power of each slash was multiplied by ten times. The ultimate move was a normal attack! One-time use forbidden technique, Eight Gates, Ye Kai. Who could block this kick of Ye Kai! As he smoked, Chen Xuan realized that there was no one else who could stand shoulder to shoulder with him. He was the only one in the world! You can read these novels on Qidian Chinese Network.
For a 'Kamen Rider crossover feudal Japan' fanfic, a Kamen Rider would be a must - have main character. In addition, a ronin, a masterless samurai, could be another main character. This ronin could have his own code of honor and be very skilled in combat. He and the Kamen Rider might meet in a dangerous situation, like being chased by bandits. And there could also be a young princess who is caught in the middle of a political intrigue in the feudal court. The Rider and the ronin might end up protecting her and in the process, get involved in the larger events of feudal Japan.
A plot could involve a Kamen Rider who has the ability to use chakra like in the Naruto world. He meets Naruto and they exchange their skills. The Kamen Rider teaches Naruto about his technology and fighting style, while Naruto teaches the Kamen Rider about ninjutsu. Then they have to face a powerful villain who is after the unique combination of their powers.
One great Naruto Kamen Rider Gaim fanfic is 'The Crossover Quest'. It combines the unique elements of both universes really well. The characters from Naruto interact with the Kamen Rider Gaim characters in a very engaging way, and the plot is full of action and mystery.
One common theme is the power combination. Writers often like to combine the powers of Naruto characters and Kamen Rider powers. For example, Naruto with the power of a Kamen Rider could create some really cool combat scenes.
The unique feature is the combination of two very different universes. Kamen Rider has high - tech gadgets and unique transformation sequences, while Naruto has ninjutsu and the chakra system. In fanfics, these elements are often mashed up. For example, a character might use a Kamen Rider - style transformation to enhance their ninjutsu.
Another option could be a new character created specifically for this fanfiction. This character could have the ability to manipulate both the ninja and the Ghost Rider elements, and wants to use that power to rule over both worlds. So, they would be the main adversary that Naruto and others have to face.
It could be one of the well - known kamen riders like Kamen Rider Decade. Since he has the ability to travel through different worlds, it would be plausible for him to end up in the world of Highschool DxD. He could use his powers to adapt to the new environment and deal with the various challenges there.