Perhaps a plot where the human - like aliens are being hunted by an evil organization that wants to study and use their powers. They have to rely on their wits and the help of a few trusted humans. Diamondhead as a human could use his crystal - like skin ability in creative ways to defend against the hunters. And they could also start to question whether they are more alien or more human as they fight for their freedom, which would be a great exploration of identity in the context of this fanfic.
In this fanfic, the relationships among the Omnitrix aliens - as - humans would be full of surprises. The competitive relationships between some aliens might turn into friendly rivalries. Take Diamondhead and Four Arms, for instance. As humans, they might compete in sports rather than in battles. Their relationships with humans who don't know their true identities would also be interesting. They would have to constantly lie to maintain their cover, which could lead to feelings of guilt and isolation. But at the same time, they could form deep and meaningful relationships with those who accept them for who they are, despite their secrets. This would create a web of relationships that are both complicated and fascinating to explore.
One idea could be exploring a new alien form that wasn't in the original series. Maybe an alien with the power to control time in a unique way. Another idea is to have Ben go on a mission in a completely different galaxy, facing new challenges and enemies.
You could also write a fanfiction where an OC is accidentally bonded with the Omnitrix in a way that it can't be removed. The OC then has to learn to live with it and use its powers for good, but they face challenges as they are not Ben. They might have to deal with people who are suspicious of them having the Omnitrix and also face enemies who are specifically after the device because of its new and unexpected host.
One idea could be that the Omnitrix malfunctions and gives Ben new, unexpected alien forms with powers he has to quickly learn to control. For example, an alien that can manipulate time in small bursts, which would create really cool scenarios where he has to fix things that went wrong in the past few seconds. Another idea is that a new villain is specifically targeting the Omnitrix and Ben has to protect it while also trying to figure out the villain's motives. Maybe this villain has a device that can nullify the Omnitrix's powers temporarily.
One idea could be that Ben discovers a new and powerful alien form in the Omnitrix that has abilities he's never seen before. He has to quickly learn to control it to defeat a new and dangerous villain.
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 interesting plot could be a world where cars have human - like intelligence and a human and a car form an unlikely friendship. They go on adventures together, like a road trip across the country, facing various challenges along the way such as bad weather and mechanical problems. Another idea is that in a post - apocalyptic world, humans rely on self - aware cars to survive. The cars protect the humans from dangerous gangs and help them find resources.
One idea could be that the aliens are actually friendly but are misunderstood at first. They came to Earth to learn about human emotions and end up helping the family in the attic deal with their own internal problems.
One interesting storyline could be about Ben exploring new alien forms that were previously unknown in the official series. Maybe he discovers a form that has unique powers that he has to learn to control quickly to face a new and powerful enemy.
One idea could be that anthros have their own society within the human world. For example, they could have special jobs like being in an all - anthro construction crew that builds unique structures using their natural abilities. Another plot could involve an anthro - human friendship where they team up to solve a mystery in their town, like strange disappearances that are somehow related to a hidden power that only the anthro's unique senses can detect.