One possible plot could be that Ben and Kai team up to fight a new alien threat that is too powerful for Ben to handle alone. Kai's combat skills and Ben's alien forms combine to create a dynamic duo. They might start off not getting along well, with Kai being frustrated by Ben's sometimes over - confident attitude while using his alien powers, but as they face challenges together, they learn to respect each other's strengths.
Perhaps in the fanfic, Kai discovers a new alien species that is related to one of Ben's forms. She decides to investigate it on her own at first, but gets into trouble. Ben then has to transform into different aliens to rescue her. Along the way, they uncover a conspiracy that involves the new alien species and an old enemy of Ben's. As they work to stop the conspiracy, their relationship deepens.
Well, in a 'Ben 10 Omniverse Ben x Kai' fanfic, perhaps it could start with Kai joining Ben on one of his inter - dimensional adventures. Along the way, they encounter various challenges that test their relationship. Ben might use his Omnitrix in creative ways to protect Kai, and in the process, they realize their mutual attraction. For example, when they are trapped in a strange alien world, Ben has to transform into different aliens to find a way out while also keeping Kai safe from the local dangers.
One possible plot could be that Esther gets caught up in an alien conspiracy in the Omniverse. Ben, being the hero, steps in to save her. As they work together to uncover the truth behind the conspiracy, they start to fall for each other.
One possible plot could be that Older Ben, having experienced more of the Omnitrix's power and the perils of the universe, takes Younger Gwen under his wing to train her in her magical abilities. They might go on adventures together where Ben uses his alien forms and Gwen uses her magic to fight enemies. Along the way, they develop a deeper bond of friendship and mutual respect.
The main characters are Ben and Kai. Ben is a heroic figure with the Omnitrix, which is a device full of alien DNA that he can use to transform. He is brave and always ready to protect the Omniverse. Kai, on the other hand, is a feisty and determined character. She brings her own charm and abilities to the story. In a 'Ben 10 Omniverse Ben x Kai' fanfic, these two are the focus. Their different personalities clash and complement each other as they navigate the dangerous and exciting world of the Omniverse together.
One common theme is friendship. Since Ben and Kai are characters from the same universe, many fanfics explore how their friendship could develop over time. Another theme could be teamwork, as they might face challenges together and have to rely on each other's skills.
Mainly, it's Ben and Kai. Ben is the wielder of the Omnitrix, which is the source of his alien - transforming powers. He's always ready for action and to protect the world. Kai, on the other hand, is a character with a lot of spunk. She can hold her own in a fight and often challenges Ben. Their relationship, be it as friends or something more in the fanfic, would be a key aspect of the story with them as the main characters.
One possible plot could be that Ben Tennyson somehow ends up in the world of Fairy Tail. He could team up with Natsu and his friends to fight against a common enemy. Ben could use his alien forms to combat the dark magic threats that Fairy Tail often faces.
Perhaps in the fanfic, a strange energy wave hits Bellwood which causes some sort of connection between Ben, Gwen and a group of girls (the harem). Ben is initially confused as to how to handle this new dynamic. Gwen tries to keep everyone in line and focused on protecting the city. As they explore the source of this energy wave, they come across an ancient artifact that seems to be the cause. They must figure out how to reverse its effects while also dealing with their new relationships. There could be some sweet moments between Ben and Gwen as they navigate this new situation with the harem, and some action - packed battles against the guardians of the artifact.
One possible plot could be that Ben 10 and Mount Lady team up to fight a powerful villain that is causing chaos in their shared city. Ben uses his various alien forms to combat different threats the villain throws at them, while Mount Lady uses her size - changing abilities to deal with large - scale destruction and support Ben in battle.
One possible plot could be that Ben and the Teen Titans team up to stop an alien invasion that threatens both Earth and the Titans' city. Ben uses his alien forms to fight the various alien threats, while the Teen Titans use their unique powers and teamwork. For example, Ben could transform into Four Arms to take on a big brute of an alien, while Raven uses her dark magic to hold off other foes. They would have to learn to work together quickly, despite their different fighting styles and personalities.