Another story could be set in a post - apocalyptic world where vampires have emerged as a result of some mutagenic event related to the nanites. Rex, being the only one with the ability to control his nanites, has to find a way to coexist with the vampires. He could encounter a vampire who was once a scientist and together they try to reverse the vampiric transformation in some people.
One idea could be a crossover with Ben 10. Rex's nanites and Ben's Omnitrix could lead to some interesting power clashes and team - ups. They could face a common enemy that requires both their unique abilities to defeat. For example, an alien - nanite hybrid villain.
One idea could be a crossover where Generator Rex's nanites interact with the X - Men's mutant powers in unexpected ways. Maybe the nanites start to adapt and mimic some of the mutant abilities, causing chaos and confusion among both groups.
One idea could be that Naruto and Rex meet in a dimension where their worlds collide. Naruto's chakra powers and Rex's nanite abilities could create some really interesting battle scenes as they team up against a common enemy, like an evil organization that wants to control both their worlds.
One possible fanfiction could be about Rex's adventures in a new, uncharted area where he discovers a strange new type of E.V.O. He has to use his powers in creative ways to deal with it and learn more about this new threat or ally.
A fanfic could focus on Noah's perspective of being Rex's friend. Maybe Noah starts to feel a bit overshadowed by Rex's powers and has to deal with his own insecurities while still supporting Rex in their adventures. For example, during a mission where Rex is getting all the glory, Noah could be the one who actually figures out the key to defeating the EVO, but no one notices at first.
For a Generator Rex vampire fanfiction, when creating characters, start with the vampires. Decide if they are traditional vampires or have some unique twist due to the world of Generator Rex. For example, they could have nanite - based powers instead of just the typical vampire abilities. Make their personalities distinct. Some could be brooding and mysterious, while others could be more outgoing and friendly despite their vampiric nature.
In a fanfiction crossover, they could end up in each other's universes by accident. Ben finds himself in a world full of EVOs and has to rely on Rex to get back home. Meanwhile, Rex is intrigued by the Omnitrix and tries to figure out how it works. They face many challenges together, like dealing with Rex's old enemies who see Ben as a new target.
In a post - apocalyptic world, Generator Rex was on a mission. Rex was also exploring the same area. They both heard rumors of the Black Knight. When they finally met the Black Knight, he was not what they expected. The Black Knight had a code of honor. Rex was intrigued and Generator Rex was curious about his technology. They started to exchange knowledge. The Black Knight taught them some ancient combat techniques and in return, Generator Rex shared his knowledge of advanced machinery. Rex learned a lot from both of them and they became friends, vowing to protect the world together.
One idea could be that Rex and Breach are forced to team up against a new, powerful EVO that threatens their mutual interests. Along the way, they start to understand each other's pasts and develop a grudging respect. For example, Rex could learn about Breach's difficult upbringing in the Nanite Collective and start to see her in a new light.
Another plot could be that an interdimensional rift opens up, and it's causing chaos in both Ben's and Rex's worlds. They discover that the source of the rift is related to the technology of both the Omnitrix and the Nanites. Together, they journey through the rift to find the cause and close it. Along the way, they meet alternate versions of themselves and their friends, which adds an interesting twist to the story.