Obviously, Percy is one of the main characters. There might also be his sidekick, let's say a talking animal like a fox named Finn. And perhaps there's an old mentor figure, an experienced wizard named Merlin.
I'm not entirely sure about the specific 'flapjack k'nuckles back story' as it's not a widely known common knowledge. It might be from a very specific or niche piece of media.
Often, the hero in a sword novel is someone who overcomes great difficulties. Take Frodo from 'The Lord of the Rings' (although it's more of a ring - centered story with a lot of sword - related elements). He has to carry the heavy burden of the ring, face numerous threats, and still manages to be brave. His journey is full of challenges that he bravely endures, making him a marvelous hero in the context of a story with swords and battles.
One interesting plotline could be Percy getting lost in a magical forest full of strange creatures. Another might be Percy accidentally stumbling upon a hidden treasure but having to face many challenges to keep it. Maybe there's a plotline where Percy befriends an unlikely ally, like a grumpy old wizard.
I'm not sure specifically as there could be various novels related to Dragon Balls. Generally, it might be about the adventures of the characters in the Dragon Ball universe, their battles to collect the Dragon Balls, and the use of the wishes granted by the Dragon Balls. It could also involve the growth of the main characters like Goku in terms of their power and relationships.
It's completely fictional. The show's plot and characters were developed by the writers' imagination rather than being based on real-life events or people. But it still manages to capture the audience's attention with its charm and humor.