[The following is a first attempt at a DBZ fanfiction, bear with me please. I know it's totally canon shattering, but it involves an original being the hero rather than someone else. This may possibly stretch into the late or even the end of the Buu saga, I don't know as of yet.]
Kafar let out a grunt as Cell stomped down on his chest. "K.O!" The perfected android shouted. "I win... perfect." He added on, a cocky smirk forming on his face. Kafar simply stared up at Cell, and quickly raised his arm with a fluid motion. He launched a ki blast that knocked Cell onto his back. Kafar quickly hopped to his feet, his body covered in bruises and scratches. His spiked brown hair had turned to a mess, and his matching brown eyes shone with hope. His skin was pale, and he donned a outfit similar to Goku's. "I'm... I'm not letting you win Cell!" He shouted. Around the arena of the Cell Games laid the bodies of Yamcha, Tienshinhan, Piccolo, Krillin, and Gohan. Vegeta and Trunks were all that remained, despite the both of them being unable to even move. Goku hadn't even entered the battle. He stood at the edge of the ring, watching his apprentice carefully. Cell stood up, gritting his teeth. "You... are a stupid, stupid boy!" Cell bellowed at Kafar. Kafar grinned, and took a fighting pose. He slowly opened his mouth, glaring at Cell. "K... Kaioken!" Kafar shouted. His body exploded into a red aura as a small smile came across Goku's face. Kafar dashed forward, swinging a punch. Cell caught Kafar's hand, and with a fluid motion, slammed him to the ground. "Oh Goku... I believe you should come pick up this garbage." Cell chuckled out, kicking Kafar to the edge of the ring. Kafar hit the ground with a thud, as he coughed out a bit of blood. "B... Bastard..." Kafar choked out, rolling onto his stomach. He got on his hands and knees, and clenched a hateful fist. "What was that?" Cell asked sarcastically, stepping closer. "I couldn't hear you over the sound of me winning." Cell added on, chuckling to himself. "Stop it Cell." Goku said from the side of the ring. His voice was stern and demanding. "You've killed enough people. I'm taking control here." Goku said, continuing his sentence as he climbed into the ring. Kafar looked up at his master, who was clearly upset with his performance. Kafar sighed in relief, and rolled out of the ring. "Ka...Kakarot..." Vegeta had somehow managed to cry out. "You'll... You'll get yourself killed..." He cried again, sitting up with the last of his strength. Goku looked at Vegeta with a smirk, as his body lit up in a golden aura. His hair spiked up, turning a bright yellow as his eyes adopted a new green color. Goku was ready to end it all.
"I've let this go on for long enough Cell. You've killed my son, my best friends, and you almost killed my apprentice." Goku shouted as the aura around his body grew larger. "It's over! I'm putting an end to this horror!" Goku shouted. He flew forward, punching Cell in the stomach. Cell groaned loudly, blood erupting from his mouth. "No more death!" Goku cried, punching Cell on the side of the head. Cell flew towards the corner of the ring, hitting one of the towers. "The whole world is sick of you!" Goku bellowed. He flew toward Cell, but Cell had a different plan. Cell dodged, causing Goku to hit the tower. Goku stepped back after slamming into the tower at full speed, and Cell extended his tail. He bashed Goku across the midsection with it, sending him soaring to the center of the ring. Kafar stood outside the ring, watching the whole thing happen. He slowly raised his hands up, closing his eyes. "Please... people of the universe, lend me your energy." Vegeta and Trunks watched in awe from the ground, as Goku stayed distracted by Cell. Goku let out a cry as Cell slammed him headfirst into the arena floor, his golden aura vanishing. His hair turned black as well. Cell pulled Goku's head up, his face bloodied. Goku shouted, and broke free of Cell's grip. Cell stepped back gracefully, as Goku got to his feet. "D-damn it..." Goku muttered, wiping some blood from his forehead. Kafar still stood with his hands raised. All he could do was watch as he gathered the universe's energy. Goku let out another cry as Cell drove a knee into his gut. Kafar cringed a little, and mumbled to himself. Goku shouted as he turned Super Saiyan once again, and punched Cell. Goku's fist hit Cell in the forehead, as Cell flew back from the force. "Still a bit of fire left in you..." Cell said, smirking at Goku. Goku glared at Cell, and smiled. "I'm only warming up" Goku muttered out, taking a fighting pose.