One common theme could be adventure. Given the DC universe setting, stories might involve Ben Turner and Vixen going on various exciting quests. Another theme could be the exploration of their powers and how they interact with each other in different situations.
Another theme could be redemption. If either of the characters has a troubled past, the fanfic could explore their journey towards redemption. For example, if Ben Turner has some past actions he's not proud of, his relationship with Mari could be part of that path to making amends. Also, a theme of discovery could be present. They could be discovering new powers or aspects of the DC universe together.
One idea could be Ben Tennyson getting transported to the DC universe and his Omnitrix's powers attracting the attention of various female characters. For example, Wonder Woman might be intrigued by his unique abilities and his sense of justice. Another could be that he teams up with some of the female superheroes to fight a common enemy, and during the process, a harem - like relationship starts to form.
Well, there's 'Ben 10 and the Justice League'. In this fanfic, Ben teams up with the Justice League to fight a common enemy. It has great character development and a really engaging plot. Also, 'Ben 10's DC Adventure' is quite good. It takes Ben on a journey through the DC world, facing off against various villains while making new friends among the heroes.
I'm not sure about specific 'ben turner vixen dc fanfic' works. You could try searching on fanfic websites like Archive of Our Own. They usually have a wide variety of fan - created stories related to DC characters.
Wonder Woman would be a great choice. She's a strong, iconic character. Her sense of honor and justice could be drawn to Ben's own heroics. Another could be Harley Quinn. Her chaotic nature might be interested in Ben's wild alien forms and adventures. And of course, Supergirl. Her superpowers and kind heart could make for an interesting dynamic with Ben.
One idea could be that Ben, with his Omnitrix, somehow gets transported to the DC universe and meets various female characters. Maybe he has to team up with them to stop a common threat, and during the adventure, relationships start to form. For example, he could work with Wonder Woman, and she is initially skeptical of his powers but grows to respect him.
Wonder Woman would be a great choice. She is strong, noble, and would be an interesting contrast to Ben's more impulsive nature. Her Amazonian upbringing and values would add depth to their interactions.
First, know the characters well. Understand Ben 10's powers and his personality, as well as the DC characters' traits. Then, come up with an interesting plot. Maybe it could be about Ben getting lost in the DC universe. Next, write engaging dialogues. For example, when Ben meets Superman, what would they say to each other? Finally, edit your work to make it flow well.