Another possibility is a human. A really strong and wise human who has trained hard and has a deep understanding of the balance between good and evil. They could be selected to be the new God of Destruction, bringing a new perspective to the role compared to the more battle - hungry Saiyans or the other alien races.
It could be a Saiyan. Since Saiyans are known for their strength and love for battle. A Saiyan could be chosen to become the new God of Destruction, like Goku or Vegeta's descendant who has a unique power that makes them suitable for the role.
Maybe an unknown alien race. This alien could have some special abilities that are different from what we've seen in the Dragon Ball universe so far. Their powers could be related to energy manipulation in a way that is both destructive and creative, which is perfect for a God of Destruction.
The plot might involve the new God of Destruction facing a powerful threat that even the other Gods of Destruction can't handle. He has to gather the strength of all the Saiyans and other allies in the Dragon Ball universe. This could lead to new power - ups for characters like Goku and Vegeta as they train to fight alongside the new God.
It could be a new character. Maybe a young wizard or witch who has a special connection to the God of Destruction. They could be from a long - lost magical family that has some ancient knowledge about this being. This character would then have to navigate the dangerous world of the Harry Potter universe, dealing with both Voldemort's followers and the chaos brought by the God of Destruction.
Obviously, Gohan would be the main character as the title implies. But there could also be other characters like Piccolo. Piccolo has always been an important figure in Gohan's life, training him and guiding him. He might play a crucial role in helping Gohan understand and control his new 'heir of destruction' power.
Goku could be the main character. Since he's the protagonist in the main Dragon Ball series, it would be interesting to see him explore the concept of Souls in the FighterZ universe. He could learn new ways to use his Super Saiyan powers in relation to his Soul.
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.
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.
It could be a rogue ninja who has also harnessed the power of a god of destruction. This ninja wants to use the power to rule the ninja world and Naruto has to stop him.
Another possibility is that the most powerful character could be an ancient deity that was sealed away long ago and is now awakened in the events of the God Mission. This deity could have powers that are far beyond the understanding of the Saiyans, Namekians, and other races. It could possess the power to create or destroy entire galaxies with a single thought, and its appearance could completely change the power dynamic in the Dragon Ball Heroes God Mission.
Another great plot could involve Goku facing off against other Gods of Destruction who don't believe he's worthy of the title. This would lead to epic battles where he has to prove himself not just with his power but also his newfound sense of divine responsibility.
A character with the ability to transform into different elements like fire, water, or earth. This would add a new dynamic to the battles. Another could be a small, alien creature that has the power to control the minds of others, creating chaos among the heroes. There could also be a warrior from a lost civilization in the Macho Universe who has a unique fighting style that combines swordsmanship and Ki blasts.