One interesting storyline could be a female version of Ben having to deal with different alien cultures in the Omniverse in a more diplomatic way than Ben usually does. For example, she might use her charm and intelligence to resolve conflicts between warring alien species on a planet instead of just using brute force with the Omnitrix transformations.
Another storyline could involve the female Ben exploring a new part of the Omniverse that was previously unknown. Maybe she discovers an ancient alien civilization that has a unique connection to the Omnitrix. She then has to figure out how to use this connection to her advantage while also protecting this newfound knowledge from villains who want to misuse it.
A possible story could be about the female Ben facing off against a powerful female villain. This villain could be a former ally who has turned bad. The female Ben has to not only battle her physically but also try to understand what led her to become evil. This could involve delving into their shared past and the events that drove a wedge between them.
Well, you could write a 'ben 10 omniverse fanfiction' where Ben loses his Omnitrix and has to rely on his wits and the help of his friends to still fight the bad guys. Or perhaps a story where the Omnitrix starts evolving on its own and gives Ben new and unexpected powers. Also, a plot where an old enemy from the past returns with a new and more dangerous plan.
One possible fanfiction could be about Ben and Kai going on a new adventure in the Omniverse. Maybe they discover a new alien species that is causing chaos in a far - flung galaxy. Ben uses his Omnitrix to transform into different aliens to try and stop the threat, while Kai uses her martial arts skills to fight alongside him.
Another plot might involve Ben and Kai getting accidentally transported to a parallel dimension where things are very different. They have to find a way back home while also dealing with the strange new versions of their friends and foes. Along the way, they discover new things about each other and their feelings start to change in this unfamiliar setting.
Well, one common type of story might be about new alien forms that Ben discovers in the Omniverse. In lemon fanfiction, there could be a focus on the unique powers of these aliens in unexpected situations. For example, an alien with the ability to manipulate time might accidentally send Ben to a different era within the Omniverse, and he has to figure out how to get back while dealing with the local threats.
One interesting concept could be creating new alien forms for Ben's Omnitrix that are unique to the fanfiction. Another might be exploring different relationships between Ben and his OC (Original Character) friends or foes. For example, an OC could be from a planet that has a very different culture from what Ben has encountered before, leading to interesting interactions and storylines.
One interesting crossover could be Naruto characters getting access to the Omnitrix. Imagine Naruto being able to transform into different alien forms from Ben 10's Omniverse. It would completely change the way battles are fought in the Naruto universe.
One great Ben x Kevin fanfiction could be about their adventures in a parallel dimension. In this story, they might face new aliens and challenges that test their friendship even more. Maybe they find a powerful alien artifact that only works when they combine their unique abilities, leading to a deeper understanding of each other.
Well, in a fanfiction, they could be on a mission to save a planet that is on the verge of destruction. Ben uses his alien powers to hold off the immediate threats, like asteroids or attacking creatures, while Kai tries to find the root cause of the planet's problems, which could be some sort of evil technology or a corrupt leader.
Perhaps a story where an old enemy of Ben's targets Rook to get to Ben. Ben feels guilty and protective. They go on the run, hiding in different places across the galaxy. Along the way, they meet some interesting characters who help them. In the end, they face the enemy together, with Ben using his Omnitrix and Rook using his upgraded Proto - Tool to defeat the bad guy.
Well, if Ben was kidnapped in fanfiction, his friends would probably start a huge rescue mission. Gwen would use her magic and Kevin his powers to track him down. They'd face all sorts of challenges along the way, like bad guys trying to stop them or traps set by the kidnappers.