A possible plot for a 'Ben 10 has Nemetrix' fanfic could be that the Nemetrix contains a hidden code or message. Ben accidentally activates it while trying to figure out how the Nemetrix works. This message leads him to a distant planet where he discovers an ancient civilization that was the origin of the Nemetrix technology. There, he has to face challenges and puzzles to unlock the full potential of the Nemetrix and also learn the true purpose of this alien device. Along the way, he might have to team up with some of the friendly aliens from that planet to fight off other forces who want to destroy the Nemetrix.
Well, a cool plot might be that the Nemetrix starts to bond with Ben in an unexpected way. Instead of just being a device for his enemies, it gives him access to some of the predator abilities of the aliens in it. For example, he could gain the enhanced speed and stealth of a certain predator alien. Then, there could be a race of alien hunters who come to Earth to retrieve the Nemetrix because they think Ben is misusing it.
One idea could be that Ben discovers a new alien form related to the Nemetrix that has powers he's never seen before. This form could have the ability to control time on a small scale, like freezing enemies for a few seconds. Another plot could involve the Nemetrix being corrupted and causing Ben's alien forms to go haywire. He has to find a way to fix it while dealing with villains who want to use the corrupted Nemetrix for their own evil plans.
One idea could be exploring the origin of the Nemetrix in more depth. Maybe there was an ancient alien race that created it for a specific purpose, like hunting down the most dangerous predators in the galaxy. Another plot could involve a character getting accidentally bonded with the Nemetrix and having to deal with its unpredictable powers.
One idea could be that the Nemetrix starts malfunctioning and gives the alien predators it controls some of Ben's Omnitrix powers. This would create a whole new set of challenges for Ben as he has to deal with enemies that are a strange mix of the two technologies.
Albedo could be a great main villain. Since he's always been jealous of Ben and his Omnitrix, if he got his hands on the Nemetrix, he could try to use it to create chaos. He might modify the Nemetrix to turn Ben's alien forms against him or use it to enhance his own powers in a twisted way.
A really interesting plot could involve a time - traveling aspect. Ben and Julie accidentally travel back in time to when Ben first got the Omnitrix. They have to be careful not to disrupt the timeline while also trying to find a way back to their own time. Along the way, they could meet younger versions of characters they know and have some really fun and emotional interactions. This could also lead to Ben learning some important lessons about his powers from his past self.
One idea could be Ben getting stranded on an alien planet full of strange and dangerous creatures. He has to use his alien forms in creative ways to survive and find a way back home.
Maybe a story where Ben teams up with some of his alien enemies against a greater threat in space. They could be in a situation where they have to fight a powerful cosmic entity that wants to destroy all known planets. Ben would have to convince his former foes that they need to work together by showing them the magnitude of the danger.
One idea could be Ben using his alien forms in a virtual reality gaming world. He could face off against digital versions of his enemies and have to use his unique alien abilities to progress through levels.
One idea could be Looma challenging Ben to a series of alien - based contests in her home planet. This would show off different Ben 10 aliens' abilities in a new and exciting setting.
A more character - driven plot could be about Ben trying to help an alien species that is being persecuted in the Omniverse. He uses his different alien forms to understand their culture and problems better. Along the way, he discovers that there are some dark secrets in the Omniverse's politics that are related to this species' situation. This would allow for a deeper exploration of the Omniverse's world - building and Ben's character growth.
Another plot could be that a new villain emerges who has the power to control both human and Myaxx technology. Ben and Myaxx must figure out a way to break this control and stop the villain from taking over the galaxy. They start by gathering intelligence on the villain's lair and formulating a plan that utilizes Ben's shape - shifting abilities and Myaxx's knowledge of her own technology.