One possible plotline could be that Anakin is somehow brought back to the time when Ben and Rey exist. Maybe he serves as a mentor to both of them, using his own experiences of the dark and light sides of the Force. He could help Ben fully turn back to the light, and teach Rey some ancient Jedi techniques that were lost in her own training.
Perhaps it's a scenario where they meet in a Force - related dreamscape. Ben is still conflicted, Rey is seeking more knowledge, and Anakin appears as a guiding spirit. They interact, and Anakin tells them about the true nature of the Force and how important it is to balance their emotions. Rey might try to convince Ben to follow Anakin's example of redemption.
I think it would be really interesting when they all use the Force together for the first time. Anakin with his great power, Ben with his conflicted energy, and Rey with her raw and untamed Force ability. They combine their powers to overcome a huge obstacle, like a powerful Sith entity. It would be a display of different generations of Force - users coming together, and the unique ways they each interact with the Force.
Another plot could be Ben's first day at a new kindergarten. He's a bit shy at first, but then he makes friends with a group of kids who love building sandcastles in the sandbox. They all work together to build the biggest and most creative sandcastle ever.
Another plot could be that Anakin, without Jedi training, still has a connection to the Force but doesn't understand it. He might have strange dreams and premonitions that he tries to make sense of on his own. This could lead to him seeking out different kinds of mentors, not Jedi, but perhaps old hermits or wise women in the deserts of Tatooine who have a different perspective on the Force.
Perhaps they meet in a post - apocalyptic world where they are the only ones left with medical knowledge. They have to combine their skills to save the remaining survivors. They might face shortages of medical supplies and have to improvise treatments, which could lead to some interesting character development and conflicts among them.
Perhaps in this fanfic, Anakin has developed some sort of new power or ability that protects him from getting burned. It could be related to his connection with the Force. He might have found a way to manipulate the Force in such a way that it forms a protective shield around him when the threat of burning is imminent. This new power could be a result of his continuous exploration and growth in the Force.
Another plotline could be that Mace is facing some sort of political trouble within the Jedi Order. Anakin, with his unique position and skills, steps in to help Mace clear his name or resolve the situation. For example, Anakin might use his relationship with Palpatine to uncover some secrets that can exonerate Mace. This would involve a lot of political intrigue and character - driven drama.
Another plotline could involve Ben and Albedo being forced to team up against a greater threat. They would have to put aside their differences and work together, which could lead to some interesting character dynamics as they learn more about each other.
Maybe in the 'ben 10 hypnotized fanfic', Ben is hypnotized by a mysterious force during one of his adventures. As a result, he starts having strange dreams that seem real and he's unable to transform into his alien forms properly. His grandfather and Gwen try different methods, like using ancient spells or advanced Plumber technology, to snap him out of it.
Maybe the sister is a hidden Jedi. She and Rey meet by chance and then they team up to find an ancient Jedi artifact that could save the galaxy from a new threat. They face off against various enemies, including some Sith cultists.
One possible plotline could be that Rey discovers she is pregnant and struggles with how to tell Kylo Ren. She might be worried about his reaction given their complex relationship. Another could be that Kylo Ren finds out first and then has to decide whether to support Rey or if his loyalty to the First Order gets in the way. Maybe there are also external forces that threaten Rey and her unborn child, such as other Sith or enemies of the Resistance.