Perhaps a half - alien, half - vampire hybrid. This character was shunned by both species and blames Ben for making him feel even more like an outcast. He uses his unique powers to create chaos and tries to turn Ben into a vampire - alien like himself.
One idea could be that an alien vampire infiltrates Ben's team. It pretends to be a friendly alien at first but then starts to slowly drain the energy of the other aliens. Ben has to figure out a way to expose it without endangering his friends.
There are some really cool 'Ben 10 Alien Force Fanfiction' out there. 'The Mutant Invasion' is a story where mutants from another dimension invade Earth and Ben has to use his alien forms in unique combinations to fight them. 'Gwen's New Powers' is another interesting one. It shows Gwen developing some unexpected powers and how she and Ben deal with that. Also, 'Kevin's Redemption' is a story that focuses on Kevin trying to make up for his past mistakes.
Some of the alien characters themselves, like Heatblast or Four Arms, are also popular. Their unique physical characteristics and powers make them interesting to write about. For instance, Heatblast's ability to control fire can lead to all kinds of scenarios, from battling fire - based villains to using his heat to solve environmental problems in a story.
One common theme is friendship. The female alien often forms a strong bond with Ben, and they support each other through different situations. Another theme is power. The female alien usually has some unique power that plays an important role in the story.
One common theme is the clash between Ben's world of aliens and the world of vampires. Another is the idea of power struggle. Vampires are often depicted as having their own set of powers, and when they cross paths with Ben and his Omnitrix, there's a struggle for dominance. Also, themes of friendship or enmity can be common, like a vampire becoming Ben's ally or a powerful enemy.
One common theme is power combination. Writers often explore how the powers from Naruto, like chakra - based jutsus, can be combined with the alien powers in Ben 10 Alien Force.
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.
One interesting story could be about an alien's unique adventure on Earth. Maybe it discovers a hidden power within itself while trying to adapt to human society.
In a Ben 10 fanfiction story, the relationship between the alien and the boy can be one of mutual discovery. The boy, usually full of curiosity, is drawn to the alien's otherworldly nature. For example, the alien might have powers or abilities that the boy has never seen before. The alien, on the other hand, may be intrigued by the boy's human nature. They rely on each other. The boy can offer knowledge about Earth, like where to find food or shelter. The alien can use its powers to protect the boy from danger. It's a relationship based on adventure and learning from each other.