Goku would be a great main character for a Dragon Ball Z haircut fanfiction. His wild hair is such an iconic part of his look. You could write about how a new adventure changes his view on his hair and he decides to get a different style. Maybe he wants to look more like the people on a new planet he visits.
Vegeta could also be the main character. He is very proud of his appearance. A fanfiction could revolve around him having his pride challenged when his hair is accidentally damaged in a battle. He then has to deal with getting a new haircut which he initially hates but later realizes gives him a new edge in combat. He could also struggle with how others perceive his new look.
Goku could be an interesting main character in a vampire fanfiction. Imagine Goku having to deal with the newfound thirst for blood while still trying to protect the Earth. His strong moral compass would be put to the test as he battles against his vampire instincts.
One idea could be a fanfiction where Vegeta gets a completely new haircut as a part of a disguise during a mission on a new planet. Maybe he has to blend in with the locals who have a very unique and flamboyant hairstyle. Another could be about Goku getting his hair cut by Chi - Chi because she wants him to look more presentable for a family gathering, but then he discovers that his power level is affected in some strange way. And a third idea might be a story where Trunks experiments with different haircuts to impress a new love interest in his timeline.
Super 17 himself could be the main antagonist if the fanfiction focuses on his corruption. He could be consumed by power and decide to rule over the universe. His already - formidable powers would make him a terrifying opponent for the Z - fighters, and they would have to find new ways to stop him without relying too much on their usual techniques.
It could be Orochimaru. In this fanfiction, Orochimaru might hear rumors about the Dragon Balls and their power to grant wishes. Since he is always seeking power and immortality, he decides to hunt for the Dragon Balls. However, because Naruto is so focused on his own battles against Orochimaru in the ninja world, he fails to realize that Orochimaru's new goal involves the Dragon Balls and the entire Dragon Ball Z universe could be at risk.
Maybe an evil scientist who has created a new form of bio - weaponry. He targets Gohan and Lime because they pose a threat to his plans of world domination. His creations could have abilities that are a challenge for Gohan and Lime to counter.
Perhaps a new Saiyan from Planet Vegeta who was sent away as a baby before its destruction and now returns to Earth in the next generation. He could bring with him a different perspective on Saiyan culture and power. He might have been trained in a different way on the planet he grew up on, and his arrival could stir things up among the Earth - based Saiyans.
The main characters for Dragon Ball Z Gine fanfiction would be Gine first and foremost. Gohan, being Goku's son, could play an important role. Videl, as Gohan's love interest, could also be in the story. Trunks, whether from the future or the present, is another option. And of course, Master Roshi. He has a vast knowledge of martial arts and could be a mentor - like figure to Gine or someone she has to interact with in the story.
Goku could still be the main character even in a dimension - hopping fanfic. His adaptability and thirst for stronger opponents would make him a great fit to explore different dimensions.
The main character could be a Saiyan gamer who was born on Earth but discovers his Saiyan heritage through the game. He then uses his knowledge of the game to train faster and become stronger than he ever thought possible, kind of like Gohan but with a more gamer - like approach to his training.
It could be a rogue Saiyan from a forgotten part of the Saiyan history. This Saiyan might have a grudge against the Z - fighters and their descendants, like Pan. He could have developed his own version of the Super Saiyan 4 power in a more evil way and wants to prove his superiority by defeating Pan.