A cool fanfiction could be about Naruto being transformed into a Kamen Rider by some strange ninja jutsu gone wrong. He has to learn to control his new Rider powers while still being a ninja, and he might even use his Rider form to bring a new sense of hope to the Hidden Leaf Village.
One idea could be that Naruto gains the power of a Kamen Rider. He could use the Rider's abilities in his battles in the ninja world. For example, using the Rider's speed to outmaneuver his opponents during a fight against Akatsuki members.
Perhaps a story where a Kamen Rider from another dimension arrives in the Naruto universe. The Rider teams up with Naruto to stop a new threat that neither could face alone. They combine their unique skills, like Naruto's shadow clones and the Rider's finishing moves.
One interesting idea could be a crossover of the Ghost Rider's powers with Naruto's ninja abilities. For example, Naruto might gain the ability to use the Ghost Rider's chain attacks in his combat style. It could also explore how the two different worlds' moral and ethical concepts interact when these two characters' stories merge.
Perhaps in this fanfiction, there could be a scenario where Naruto has to team up with some of his friends to take on Ghost Rider. They would have to figure out Ghost Rider's weaknesses, which could be a mix of things from both the Naruto universe and what we know about Ghost Rider. And along the way, they might learn some new things about their own powers too.
One idea could be Naruto using his dragon to quickly travel across the ninja world for missions. His dragon could also have unique abilities, like breathing a special type of chakra-infused fire that can counteract certain jutsu.
Maybe in the fanfiction, Wolf is actually an undercover agent sent to protect Alex Rider without his knowledge. As they interact, there are misunderstandings at first. Alex thinks Wolf is a threat, but then they discover a common enemy. Their relationship then develops into a strong alliance as they work together to take down the bad guys, with Wolf teaching Alex some of his more unorthodox combat techniques along the way.
Maybe Flynn Rider is on a quest for a rare jewel and it leads him to Arendelle. There, he encounters Elsa. Elsa is initially afraid she might accidentally harm Flynn with her powers. However, Flynn is intrigued by her powers and helps her see that they can be used for more than just isolation. They could team up to protect Arendelle from an approaching threat using Elsa's powers and Flynn's street - smart skills.
One idea could be that Naruto somehow inherits the Ghost Rider bloodline. He could then use the powers of the Ghost Rider in his battles in the Naruto world. For example, his Rasengan might be infused with the hellfire of the Ghost Rider, making it an even more powerful attack.
A plot could involve a magical accident that fuses Naruto and Ghost Rider's essences. This new being has a strange allure and power. In the Naruto universe, female characters start to gather around this new entity. There could be a lot of drama as the harem members come from different ninja clans and have different motives. Some might be in it for the power, some for true love, and they all have to deal with the challenges that come with this new and powerful being in their midst.
One idea could be that Ghost Rider somehow gets transported into the Young Justice universe. He might initially be seen as a threat by the team. But then they realize he's fighting against a common evil that has ties to the dark forces in both their worlds. For example, a demon that is trying to open a portal to bring more chaos.
One idea could be that Ghost Rider somehow gets transported to the world of Fire Force. He could team up with the Fire Force members to fight against a new type of infernal that has powers related to the underworld. His Penance Stare might be used to expose the true nature of some of the more mysterious infernals or even some corrupt individuals within the Fire Force organization.
You could write a fanfiction where Alex Rider has to go undercover in a school as a normal student, but he discovers a secret society within the school that is involved in some sort of illegal activity. This would be a different kind of mission for him, as he's used to more international espionage. He would have to use his wits and skills in a more confined and familiar setting.