Well, if it's a crossover with Ultraman, Ultraman could be a great addition. His super strength and light - based powers would contrast well with the Jetman's abilities. They could have a friendly rivalry at first but then team up to face a powerful kaiju that is threatening both their worlds.
A crossover with a superhero universe like the Marvel or DC. For instance, the Jetman could cross paths with Iron Man. Tony Stark could be intrigued by the Jetman's technology and they could end up working together to upgrade their respective suits. Or perhaps they find themselves in a situation where they have to save the world from an alien invasion that targets both their dimensions.
I think it could be about the journey of the Jetman. We might get to know how he started, his training, and all the challenges he overcame to be able to do what he does. Maybe it will also show some of his most memorable flights and the places he has flown over.
Another idea is that Greninja gets exposed to some kind of meta - human - creating substance in the DC universe and gains new powers. It could then join the Teen Titans, sharing its unique Pokémon abilities with the group. It would be interesting to see how Greninja interacts with characters like Robin, Starfire, and Cyborg, and how it uses its powers in battles against the Titans' enemies.
In this fanfiction, Skynet could find a way to connect to the Matrix. It might try to take over the Matrix and use it to control more humans. The machines in the Matrix might initially resist, but Skynet could offer them a deal to share power over humanity.
Crossover fanfiction is fan - made content that blends aspects of distinct fictional realms. It can be really exciting as it gives a chance to see superheroes from the Marvel Universe interact with characters from a classic novel like 'Pride and Prejudice'. This form of fanfiction often appeals to a wide range of fans who enjoy different types of fictional works and like to see the collision of different ideas and concepts.
A '24 crossover fanfiction' is a type of fan - created work that combines the elements of the '24' franchise with other fictional universes or characters. It allows fans to explore new storylines and interactions that wouldn't occur in the original '24' series.
One idea could be that Greninja, being a ninja - like Pokémon, somehow gets transported to the Naruto universe. It could team up with Naruto and use its water - based attacks in combination with Naruto's Rasengan. Maybe Greninja's ability to blend into the shadows could be used in stealth missions in the Hidden Leaf Village.