Gara and Four Arms would have an interesting interaction. Gara, with his sand powers, is used to being in control and a bit of a loner. Four Arms is all about brute strength and action. When they meet, Four Arms might challenge Gara to a test of strength, which Gara would initially be hesitant about. But then they could find common ground in protecting their respective worlds. Four Arms could show Gara a more straightforward way of fighting, while Gara could teach Four Arms about using the environment to his advantage with his sand.
One possible plot could be that Naruto and Ben Tennyson are somehow transported to each other's universes. Naruto, with his ninja skills, could be intrigued by Ben's alien forms and their powers. Ben, on the other hand, would be amazed by the chakra system in Naruto's world. They might team up to fight a common enemy that threatens both their worlds, like an alien force that has found a way to use chakra for evil purposes. This would lead to a lot of action -filled scenes where Naruto uses his jutsus and Ben transforms into different aliens to combat the threat.
One common theme is power combination. Writers often explore how the powers from Naruto, like chakra - based jutsus, can be combined with the alien powers in Ben 10 Alien Force.
One idea could be exploring the backstories of the aliens more in - depth. For example, how did Four Arms become so strong? Another could be a story where Ben has to team up with his enemies to fight a greater threat. Maybe Vilgax and Ben have to work together against an even more powerful alien race.
In Ben 10 Alien Force OC fanfiction, there are several engaging concepts. One is the concept of OCs having a hidden agenda. For instance, an OC might seem friendly at first but is actually working for an evil organization. This creates a sense of mystery and suspense. Another concept is the cultural differences between the OCs and the regular Ben 10 aliens. If an OC is from a highly advanced and peaceful society, their values and reactions to the chaos in the Ben 10 world can be very different, which can be explored in interesting ways in the fanfiction.
Ben Tennyson would most likely be one of the main characters as he is the central figure in the Ben 10 series. Gwen, his cousin, and Kevin, his friend, are also likely to be main characters. They often accompany Ben in his adventures in the Alien Force series.
I think the interaction between Ruby and Ben would be really interesting. Ruby is very energetic and has a strong sense of justice. Ben, with his experience of using the Omnitrix to save the day, could share some of his stories with her. They could also have some friendly competitions regarding their combat skills, like who can take down a group of Grimm faster, with Ruby using her Crescent Rose and Ben using one of his alien forms.
There are some really cool 'Ben 10 Alien Force Fanfiction' out there. 'The Mutant Invasion' is a story where mutants from another dimension invade Earth and Ben has to use his alien forms in unique combinations to fight them. 'Gwen's New Powers' is another interesting one. It shows Gwen developing some unexpected powers and how she and Ben deal with that. Also, 'Kevin's Redemption' is a story that focuses on Kevin trying to make up for his past mistakes.
The interactions between the Blue Ranger from Mystic Force and the Blue Ranger from SPD could be really interesting. They might start off a bit competitive, trying to show off their respective skills, but then learn from each other.
All Might and Ben would have a great interaction. All Might, being the symbol of peace in the MHA world, would be intrigued by Ben's powers. He might see Ben as a young hero with a different kind of power set. Ben, on the other hand, would look up to All Might's heroism. Also, Ochaco and Ben could have an interesting dynamic. Ochaco's gravity - controlling Quirk could be used in combination with some of Ben's alien forms in creative ways during battles or rescue operations.
Well, aside from the main trio, characters like Vilgax are often included. He's a powerful villain and can create a lot of conflict in the story. Grandpa Max is also a good character to add. His wisdom and experience can guide Ben in difficult situations. And then there are the aliens themselves. For example, Rath is a very popular alien form of Ben, and fans like to write stories that focus on his wild and unpredictable nature.