One interesting 'Dragon Ball Z Human Fanfic' story could be about a human character who discovers they have latent Saiyan powers through some strange genetic quirk. They then have to learn to control these powers while dealing with the normal human world around them.
First, you need to know the Dragon Ball Z universe well. Understand the power levels, the different races, and the existing storylines. Then, create interesting human characters with their own backstories, motives, and personalities. For example, you could make a human character who is a scientist trying to understand the Saiyan biology.
One alternative is to focus on character backstories. You could write about the early days of Piccolo, how he came to be the way he is. Another option is to do crossovers with other non - sexual universes. Maybe a story where the Dragon Ball Z characters meet characters from a magical anime world and they have to work together to solve a problem. Also, you can write about the relationships between the characters in a platonic way, like the deepening of the friendship between Gohan and Krillin.
Some 'Dragon Ball Z Fanfic' worth checking out are 'The Lost Saiyan'. This fic tells the story of a Saiyan who was lost in space and finally makes his way to Earth. 'Piccolo's Secret Training' is another one. Here, Piccolo undertakes a training that could change the balance of power. And 'The Dragon Ball Hunt' is an exciting fanfic where characters are on a quest to find all the Dragon Balls for a very different reason than in the original.
Many Dragon Ball Z Cell fanfics might explore alternate timelines. For example, what if Cell had successfully absorbed all the Androids before facing Goku? This would have made him even more powerful and could have led to a completely different outcome for the Dragon Ball Z universe. It's exciting to think about all these different possibilities.
First, familiarize yourself with the Dragon Ball Z world, its characters, and their personalities. Then, come up with an engaging story that fits within that framework. Pay attention to the action sequences and power levels to keep it consistent with the series.
One interesting crossover could be a battle between Hulk's brute strength and Goku's Super Saiyan power. Maybe in the fanfic, they start off as rivals, with Hulk misunderstanding Goku as a threat to Earth. Their fight would be epic, with Hulk's limitless rage against Goku's increasing power levels. It could also explore how their different universes' power systems interact.
Common themes in 'Dragon Ball Z Human OC Fanfiction' include heroism. The human OCs usually end up being heroes in some way, whether it's saving a city or the whole universe. Another theme is the exploration of new powers. These OCs might discover powers that no one else in the Dragon Ball Z world has. And the theme of family also shows up sometimes. They could be searching for their lost family or creating a new family - like bond with the other characters.
One interesting fanfiction could be about a human character discovering a new form of power that is unique to humans, not Saiyan-based. For example, a story where a human martial artist figures out how to tap into the latent spiritual energy within all humans to achieve a power level that can rival the Saiyans.
Training is a key factor. In fanfictions, humans can train in extreme environments, like on a planet with high gravity. This forces their bodies to adapt and become stronger, increasing their power. Just like how Goku trained on King Kai's planet.