Gwen could be an interesting addition. Her magic powers could interact in unique ways with the time - travel concept. Maybe she could use her magic to repair time rifts that Ben accidentally creates during his travels. Also, she could provide a different perspective on the events they encounter in different times.
Vilgax would be a great character. If he gets hold of time - travel technology, he could try to rewrite history to make himself the ruler of the universe from the very beginning. Ben would then have to race against time to stop Vilgax from changing the past and destroying the future as he knows it. This would create a lot of tension and action in the fanfiction.
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.
Gwen could be really interesting. She could have developed different powers in a different time period that Ben discovers when he travels back. Also, Grandpa Max in his younger days would be cool. He might have been involved in some secret time - traveling adventures that Ben uncovers. And Vilgax from different points in time could add a lot of drama. Maybe a younger Vilgax who is still learning and more vulnerable, or an older, more powerful Vilgax from a far - off future.
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.
Ben Tennyson is definitely an interesting character to include. His ability to transform into different aliens gives a lot of possibilities for the story. Finn the Human is also great. His adventurous spirit and his sword - fighting skills can add action to the fanfiction. Jake the Dog can be really fun too, with his shape - shifting abilities. And of course, Princess Bubblegum, her intelligence and leadership can bring a different dynamic to the story.
Morgan could be an interesting addition. He might accidentally get caught up in Chuck's time - travel adventures. His comical nature could provide some light - hearted moments in an otherwise complex time - travel plot, like when he misunderstands the technology or customs of a different time.
Issei himself is of course very interesting. His reactions to different time periods and how he uses his knowledge from the future can be really engaging. Then there's Rias. Her presence can add a layer of complexity, especially if she has different relationships with Issei in different timelines. Another interesting character could be Vali. His rivalry with Issei can take on new dimensions when time travel is involved, like competing in different historical battles or for the affections of a character in a different era.
Ben Tennyson would most likely be one of the main characters as he is the central figure in the Ben 10 series. Gwen, his cousin, and Kevin, his friend, are also likely to be main characters. They often accompany Ben in his adventures in the Alien Force series.
The idea of time travel as a form of spiritual journey could be explored. In the Hobbit universe, time travel might not just be about physically moving through time but also about the hobbits connecting with their ancestors on a deeper, spiritual level. For example, a hobbit could travel back in time and meet an ancient hobbit sage who imparts wisdom that is crucial for the future of the Shire. This would blend the fantastical element of time travel with the rich cultural and spiritual aspects of the hobbits' world.
One of the most interesting characters to include would be Orochimaru. His thirst for knowledge and immortality could lead to some really wild plot twists in a future time - travel fanfiction. Then there's Shikamaru. His intelligence could be used to strategize in a future full of new challenges. And Sakura. Her growth as a ninja and her relationship with Naruto and the others could bring a lot of depth to the story.
One character that would be fascinating is Medivh. As a powerful mage with knowledge of time and magic, he could either be a helper or a hindrance to Anduin. He might know secrets about the time travel that Anduin is doing and use it to his own ends. Another interesting addition could be Illidan Stormrage. His complex relationship with power and his own past actions could make for some intense interactions with Anduin as he travels through time.
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.