The plot could center around the OC having a unique item that attracts the attention of both Ben and Gwen. This item might be a key to an ancient power or a device that can manipulate time. As they all try to figure out what the item is and how to use it, they face challenges from other alien races who also want the item. Ben uses his various alien forms to battle these foes, Gwen uses her intelligence and magic to solve the mysteries related to the item, and the OC provides insights based on its own knowledge of the item's origin.
Well, it could be about how Ben and Gwen adjust to their new roles as parents. Maybe they face challenges like protecting the baby from villains who might want to use the baby's special powers (assuming in the fanfic world the baby has some).
The plot could revolve around a tournament where powerful beings from different universes are invited to compete. Naruto, Ben 10, and Gwen all participate. Naruto showcases his ninja techniques, Ben shows off his alien transformations, and Gwen displays her magic. As the tournament progresses, they start to form alliances outside of the competition. They discover a conspiracy behind the tournament, where the organizers are planning to use the power of the participants for their own evil purposes. So, they decide to work together to stop this threat.
One possible plot could be that a new powerful alien threat emerges that neither Ben, Gwen nor Kevin can defeat alone. They have to combine their unique powers and skills. Ben could use his alien forms, Gwen her magic, and Kevin his Osmosian abilities. They start off not getting along well in the team - up, with some bickering about the best way to approach the enemy. But as the situation gets more dire, they learn to trust each other and work in harmony to defeat the foe.
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 OC's character can be developed by giving it a unique backstory. For example, if the OC is an alien, describe its home planet, its family, and what led it to cross paths with Ben and Gwen. This backstory can influence its actions and decisions throughout the fanfiction.
One plot idea could be that they finally kiss after a long period of secretly having feelings for each other during a dangerous mission. When they think they might not survive, they confess their love through that kiss.
Well, it could be about their adventures in a new world. Maybe they are all in a magical place where they have to work together to solve problems. For example, they might face some mythical creatures and have to use their unique powers to defeat them. Gwen and Gwendolyn could bring their intelligence and magic skills, while Ben uses his alien forms.
Well, one possibility could be that the baby inherits some of Ben's alien powers in a really unique way. Maybe it's not as straightforward as having the Omnitrix, but has some latent abilities that start to show as it grows. And Gwen could be teaching the baby how to control any magical tendencies it might have, since she has her own magic skills.
One possibility is that the story could explore how Gwen's personality changes when she has the Omnitrix. She might become more confident or more responsible. Also, there could be new villains who are attracted to the Omnitrix now that Gwen has it. She would then have to face these threats and protect the Omnitrix from falling into the wrong hands.
Well, they could go on adventures where their new - found feelings add an extra layer of tension. For instance, when they're in a dangerous situation, Ben might be more protective of Gwen because of his love for her.