One interesting fanfiction could be about Marron's training journey. Maybe she decides to train under Piccolo to become a stronger fighter, facing all kinds of challenges and self - discovery along the way.
One interesting storyline could be Goten and Marron teaming up for a martial arts tournament. They could face various challenges together, like tough opponents and strange tournament rules. This would show their growth as fighters and also their friendship.
In some fanfictions, their relationship could take a romantic turn. Maybe after going through a lot of adventures together, they start to see each other in a different light. They would then have to deal with the reactions of their friends and family, which would add more drama to the story.
There are no such inappropriate 'Straight Shota' stories in the official Dragon Ball Z canon. Dragon Ball Z mainly focuses on epic battles, power-ups, and the adventures of Goku and his friends to protect the Earth from various villains.
Dragon Ball Z is both anime and manga. The anime was adapted from the manga and they share the same story and characters, but presented in different mediums.
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.