Another storyline might involve the Omnitrix malfunctioning in a way that it starts fusing different alien DNA together, creating hybrid forms for Ben. This would lead to him having to adapt to these new and unexpected abilities while also dealing with the chaos it causes in his life and the world around him. For example, a fusion of a heat - based alien and a water - based alien could create an interesting power dynamic that he has to figure out.
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.
Another could be an OC with the Omnitrix getting stuck in a parallel universe where the rules of the Omnitrix are different. For example, instead of being able to transform into known aliens, the OC has to figure out how to use new and strange alien forms that are native to that universe. This could lead to all sorts of adventures as the OC tries to find a way back home.
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 interesting concept could be exploring new alien forms that the Omnitrix can transform into. Maybe there are some hidden or rare aliens that Ben discovers in the fanfiction.
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.
Maybe the male OC is from a different dimension where the Omnitrix works in a completely different way. He accidentally gets transported to the Ben 10 universe. His Omnitrix has some unique alien forms that are not known in this universe. He teams up with Ben and Gwen to fight a new common enemy that is attracted to the strange energy his Omnitrix emits. Along the way, he learns about the values of friendship and courage from them.
Some fanfictions might explore the idea of a Fem Omnitrix having unique features. For instance, it could have an enhanced ability to transform into female - only alien species. This could lead to new adventures and storylines. Additionally, the fanfiction could focus on how the female character's identity is affected by having the Omnitrix. She might struggle with the power and responsibility in a different way than Ben, which would add depth to the story.
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.
One interesting storyline could be Ben using his alien forms in a virtual gaming world to defeat a powerful digital virus. The unique combination of his real - world powers and the challenges of the game environment makes it exciting.
Another storyline could involve a love interest between Ben (in one of his alien forms) and a female alien. For example, if Ben turns into Heatblast and meets a female alien who has a natural affinity for fire - like she can control different types of flames. They start off as rivals, competing to see who can control fire better, but then gradually develop feelings for each other as they face challenges together and learn more about each other's cultures.