If Oceanus Shenron was the protagonist, he might start off as a villain - like character. But as the story progresses, his motives and actions could be more complex. For example, he could be trying to protect the Dragon Balls from a new group of villains who want to use them for evil purposes, but his methods of protection are misinterpreted by the Z - fighters at first.
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.
A Kryptonian in the Dragon Ball Z universe could potentially be a very powerful addition. Their natural abilities like super strength, flight, and heat vision could make them a force to be reckoned with. However, they would also face challenges as the Dragon Ball Z world has its own power scale with ki-based powers. They might have to adapt to the different fighting styles and power sources. Maybe they could learn to use ki in addition to their Kryptonian powers, or they could find a way to combine the two in unique ways.
In the fanfiction, Oceanus Shenron might be the only one who can stop a new type of energy - based threat that is emerging in the Dragon Ball GT universe. This energy is causing chaos and destruction, and it is slowly corrupting all the other Shenrons. Oceanus Shenron, being a unique and powerful Shenron himself, decides to take on this challenge. Along the way, he discovers secrets about his own origin and the true nature of the Dragon Balls that no one has ever known before.
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.