She could be kidnapped by an enemy who wants to use her as leverage against Gohan and the other Z - fighters. This would lead to a rescue mission where the Z - fighters have to face new and powerful foes. For instance, the kidnappers might be from a far - off planet that has a grudge against the Saiyans.
In a fanfiction, Gohan's sister could start a school for martial arts on Earth. She wants to pass on the knowledge she has learned from her family. But she faces challenges like getting students, dealing with rival martial arts schools, and also protecting the school from villains who want to disrupt it. This would show a different side of the Dragon Ball Z universe, focusing on the growth and development of martial arts on Earth from a new perspective.
Perhaps Gohan's sister has a prophetic dream about a great danger coming to Earth. But no one believes her at first. She then has to find a way to convince Gohan and the others that her dream is real. As she tries to prove herself, she discovers more about her own latent powers that are related to her prophetic abilities.
One idea could be Goku and Gohan going on a special training journey to a new planet with unique gravity and energy sources. This would force them to adapt and develop new techniques together.
One idea could be Gohan and Lime teaming up to face a new and powerful enemy that neither of them could defeat alone. They could train together, with Gohan teaching Lime some of his Saiyan techniques.
One idea could be Future Gohan training a new generation of fighters in a post - apocalyptic world. He could pass on his skills and knowledge, creating a new hope for the future. Another plot could involve him finding a way to travel back in time to prevent the events that led to his world's destruction. Maybe he discovers a hidden power within himself that he didn't know he had and uses it to fight against the remaining threats in his world.
Perhaps a story where Gohan and Videl have to team up to protect their family from a new and powerful threat that is specifically targeting them. They would have to use their combined skills and the power of their relationship to overcome it. In this fanfiction, we could see how their love for each other and their family gives them the strength to fight.
One idea could be Gohan crossing over into the Naruto universe. He could team up with Naruto and use his Saiyan powers to fight against the Akatsuki. Another plot could be Gohan in the Harry Potter world, using his ki to defend Hogwarts from Voldemort. Or perhaps Gohan in the DC universe, fighting alongside Superman against a common enemy.
One idea could be Gohan traveling back to the Saiyan - Planet Vegeta era. He could try to prevent the destruction of the Saiyans by Frieza. Maybe he'd use his knowledge of future events and his advanced power to stand up to Frieza earlier. Another plot could be him going back to a time during the Cell Games. He could train his past self more effectively, leading to an even stronger version of himself to face Cell.
A plot could revolve around Chichi wanting Gohan to focus more on his studies and less on training. This causes some tension between them as Gohan feels he needs to train to protect his family. It could show how they resolve this difference in priorities.
One possible fanfiction idea could be that Gohan's sister discovers she has a unique power that no one else in the family has. Maybe she can communicate with animals in a way that helps the Z - fighters. For example, she could get information from the animals about the whereabouts of the next big threat to Earth.
One idea could be Gohan in his Super Saiyan 4 form facing a new, powerful enemy from another dimension. He could struggle at first to control the raw power of this form while also trying to protect his friends and family. Maybe this new enemy has the ability to nullify the Saiyan's energy attacks, forcing Gohan to rely more on his martial arts skills that he learned from Piccolo.
One idea could be that Gohan discovers an ancient animal with special powers. Maybe it's a mystical deer that can enhance his ki when he's near it. Another plot could involve Gohan turning into an animal himself, like a powerful eagle, and having to learn to control his new form and its abilities. Or perhaps he befriends a group of talking animals who help him in a battle against a new enemy.