Maybe the story could be a time - travel fanfic. The DBZ girl comes from a future where Trunks and Gohan didn't survive a certain battle. She travels back in time to team up with them and change the course of history. Along the way, she has to deal with cultural differences between her future world and the present - day Z - fighters' world, and also form a bond with Trunks and Gohan.
Well, a cool plot could be that Baby Trunks is sent to an alternate dimension where everything is opposite. For example, good is bad and bad is good. He has to figure out how to survive and find a way back. Also, a plot where he befriends a creature that no one else can understand and they have to work together to overcome a powerful enemy. Maybe he gets a premonition of a future disaster and has to convince everyone to believe him and take action.
For a 'dbz gohan crossover fanfiction', a plot where Gohan crosses into the DC Comics universe would be exciting. He could team up with Superman and learn about different types of powers. Maybe he'd help Superman understand the concept of ki. Another idea is a crossover with the Final Fantasy series. Gohan could find himself in a world full of summons and magic, and use his martial arts to fight alongside the Final Fantasy characters.
One idea could be Trunks traveling to an alternate universe where the rules of DBZ are slightly different. For example, the Saiyans never lost their planet but have a different culture. Another could be Trunks teaming up with a character from a different anime in the Dragon Ball Z world to fight a new, powerful enemy. Maybe a character from Naruto who has unique jutsu skills that could combine with Trunks' power in an interesting way.
One plot idea could be that Gohan and Trunks team up for a martial arts tournament. They train together, sharing their unique skills and techniques. During the training, they face various challenges that test their friendship and determination.
Bulma is often a popular character in fanfiction involving Trunks and Gohan. Since she is Trunks' mother, she can play an important role in stories. For example, she might be creating new technology to help them in their battles.
Perhaps a plot where Future Gohan and Future Trunks accidentally travel to an alternate timeline. There, they have to team up with different versions of themselves to defeat a common enemy. This would involve exploring how they interact with these alternate selves and how they adapt to the new environment and challenges.
Maybe a fanfiction set in an alternate universe where Gohan and Trunks have to protect a group of survivors in a post - apocalyptic world. Their different personalities, Gohan's calmness and Trunks' impulsiveness, create both tension and cooperation as they fight for the safety of the group.
One interesting dbz trunks fanfiction could be about Trunks' time - traveling adventures in more detail. Maybe it focuses on his experiences in the past and how they shape his character in the present. For example, his interactions with the Z - fighters in the past timeline and how that knowledge helps him in his own time.
Another interesting plot could be Vegeta and Little Trunks getting lost in an unknown part of the universe during a training journey. They would have to rely on each other to survive and find their way back home. Along the way, they might encounter new species and face challenges that would test their relationship and skills.
Well, perhaps the OC is a scientist who was involved in the creation of Android 21 in some alternate universe. They could have a shared history that neither of them fully remembers at first. Or the OC could be a martial artist who challenges Android 21 to a fight not realizing her true power. This could lead to a series of events where they end up training together and learning from each other.