Hello! This is a novelization of the wildly popular manga/anime Dragon Ball Z. I know this has probably been done, but I wanted to offer my own take on this idea. We will start at the beginning of DBZ, after Goku has defeated Piccolo Junior, mostly since I'm not familiar enough with the pre-Z story to novelize it well. I'll mostly be going off the manga, but don't kill me if I just happen to include some anime-only content. With that out of the way, let's begin!
Son Goku was the world's strongest man and greatest hero. With any luck, he was also about to win the 23rd Tenkaichi Budokai, the biggest martial arts tournament in the world. Right now, though, all of his limbs were broken, and his arch-enemy had just fired a ki blast at him. He could hear his friends screaming, but there was nothing they could do against Piccolo, King of Demons.
"I did a far more thorough job at breaking you than even my father! There's no way out of this one!" Piccolo laughed horribly as the blast hit Goku and destroyed what little was left of the arena. He flew down to make sure his enemy was dead. "Cry all you want, you pathetic humans. Your savior is nothing but ash, and there is not a damn thing you can do about it ! Now and forever, Son Goku is dead!"
Just a few feet away, the humans were white with fear. Krillin was in shock. "He... He killed Goku... This can't get any worse!", and Roshi knew it was true. Tenshinhan was the strongest of them, and he knew the Mafuba to imprison Piccolo, but even if he could survive the move, Piccolo would kill him in a single blast. "Ha ha! Now that Goku is dead, I can build my world of chaos! Who's going to stop me? Certainly not you."
Piccolo went on, but the others were too busy looking at a speck in the sky. It was falling, it was almost like it was aimed at the demon king, and it vaguely resembled-
"Tenshinhan, you have three eyes. Does that look like-" "Yes, Krillin! It's Goku!" Piccolo had forgotten that he wasn't the only fighter who knew how to fly. Now, Goku was dive-bombing towards the demon, and by the time Piccolo looked up, it was far too late. "It's over, Piccolo!", Goku shouted as he hit Piccolo hard enough to knock him out.
"Judge, he's- he's out of the ring, isn't- isn't he?" Goku asked. All the spectators had run away long ago, but miraculously, the tournament announcer had stayed to watch the fight. "Wha- what? Well, yes, I guess he is! The winner, and twenty-third world martial arts champion is... Son Goku!" All of Goku's friends crowded around him and congratulated him, and as Yajirobe handed him a Senzu, Goku wanted to feel this way for the rest of his life.