Obviously, Gohan is the main character. But often, you'll also see characters like Piccolo. Piccolo might be a mentor - like figure, giving Gohan advice on how to handle his new dragon master powers.
Another common main character is Videl. She could be Gohan's love interest and also get involved in his dragon master adventures. For example, she might help Gohan research about the dragons' history.
One interesting fanfiction could be where Gohan uses his dragon master powers to protect the Earth from a new, unknown threat. Maybe he discovers a new type of dragon that has different abilities and he has to learn how to work with it quickly.
The main character is the dragon master, no doubt. He or she is the one around whom the story revolves. Besides, there may be antagonists who are against the dragon master's control over the dragons. These could be other humans who fear the power of the dragons or want to use them for evil purposes. And the dragons, whether they are a single dragon with a special bond to the master or a group of dragons, are also main characters in the sense that they are central to the plot and the dragon master's story.
Since I don't know the exact 'dragon master novel', it's hard to say. But typically, there would be the dragon master themselves. There might also be the dragons which could have distinct personalities. And there could be a mentor figure who helps the dragon master in their journey.
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.
Sasuke might also be involved. He could be initially skeptical of Naruto's newfound dragon powers, creating some tension. But as the story progresses, they might work together. Another possible character could be Kakashi, who serves as Naruto's mentor. He would guide Naruto in understanding and controlling his dragon - related abilities, like teaching him how to combine dragon techniques with his ninja training.
Most likely, the dragon master is a main character. There may also be the dragon itself as a significant character.
I don't know for sure as I haven't read it. But it's likely to have the dragon master as a main character. There may also be the dragons themselves, each with their own personalities.
Often, his friends at high school can be important characters too. They might be normal humans who are curious about Gohan's sometimes strange behavior. And of course, his family members like Chi - Chi could make appearances, maybe giving Gohan advice on how to balance school and home life.
In most 'Lucy the Lightning Dragon Slayer' fanfictions, Lucy herself is front and center. But we also see a lot of the guild master, Makarov. He is often the one guiding Lucy in her journey with her new powers. He gives her advice on how to control it and use it for good. And then there are the other guild members. Happy, for example, might accompany Lucy on some of her adventures and provide some comic relief. The villains in these fanfictions also become important characters as they are the ones that Lucy has to face off against with her lightning - based powers.
Well, Cabba himself is obviously a main character. He's the Saiyan from Planet Sadala. Goku often appears too as he has a big influence on Cabba. He's like a mentor to Cabba in many ways.