One idea could be Ben going back in time to prevent an alien invasion that in the original timeline led to the destruction of his hometown. He could use his ultimate alien forms in creative ways to outwit the invaders before they even start their attack.
Perhaps Ben travels to the future and discovers that his actions in the present have led to a dystopian world. He then has to go back and change certain events. For example, he might find that an overuse of his alien powers has caused an imbalance in the ecosystem, so he has to be more careful about how he uses them in the past to avoid this future.
Definitely Ben himself. His ability to transform into different aliens makes for interesting scenarios in different time periods. For example, in the past, he could transform into an alien that was thought to be a myth, causing all kinds of chaos or amazement.
I'm not entirely sure as it could be a very specific or fan - made story. But generally in the Ben 10 Ultimate Alien series, Ben Tennyson has a new Omnitrix which gives him access to ultimate forms of his aliens. The big story might involve him facing new villains, protecting the Earth and the galaxy, and dealing with the consequences of using his powers.
I'm not entirely sure about the exact plot details of 'ben 10 ultimate alien the big story'. It might involve Ben Tennyson using his various alien forms to face some big threats and challenges, but that's just a general guess.
One idea could be Ben traveling back in time to meet his younger self and having to hide his identity while trying to prevent a future villain from getting a powerful weapon in the past. Another could be Ben traveling to different time periods in the Ben 10 universe to gather artifacts that are needed to stop an all - powerful time - traveling enemy in the present. Or he could accidentally end up in a time where the Omnitrix doesn't exist yet and has to find a way back while dealing with the different power dynamics of that era.
Well, perhaps the kids travel to a time when the Avengers were just being formed. They meet the younger versions of their heroes and end up having to help them in a mission that was previously unrecorded. This would add a new layer to the Avengers' backstory and give the kids a chance to prove themselves. They could also learn valuable lessons from the early Avengers about teamwork and sacrifice.
One idea for a Ben 10 Ben and Young Gwen time travel fanfiction could be that they travel back to the time when the Omnitrix was first created. They could witness the origin of the device and perhaps even meet the aliens who had a hand in its creation. This could lead to them learning secrets about the Omnitrix that they didn't know before, which could help them in their present - day battles.
Well, it might be about how time heals the wounds or problems within the Ben 10 Alien Force universe. It could be that characters who had conflicts in the past are brought together by some time - related event. For example, perhaps an old villain returns but through the passage of time, Ben and his team have grown stronger and more united, and they use this new - found strength to face the threat. They might also discover something about the origin of their powers or the history of the aliens that is related to time.
Another great time - travel scenario could be Ben going to a future version of the Omniverse. He could see how his actions in the present have affected the future. He might discover new forms of the Omnitrix or new allies and enemies that have emerged as a result of his present - day decisions.
One idea could be that Ben has to adapt to the daily life of the alien he's stuck as. For example, if he's stuck as a Four Arms, he has to deal with constantly breaking things because of his size and strength. Another could be that he has to find a way to communicate with his friends and family in his alien form, which might be difficult if the alien has a different language or way of expressing itself.
One idea could be exploring Alien X's internal conflict between Bellicus and Serena in a new situation. For example, when faced with a moral dilemma on a planet where two species are at war and both have valid reasons for their actions. Another plot could be Alien X having to deal with a powerful new enemy that can somehow disrupt his omnipotent powers. Maybe this enemy has the ability to split Bellicus and Serena's consciousness further, causing chaos within Alien X.