Kuririn is dead. Son Gohan's dragon ball is stolen. And the Tenka-ichi Budokai's participant roster has been taken. Mr. A tells our heroes that Kuririn fought against a monster, but was overtaken and killed.
Goku cares little for the reasons why. Tying his Nyoibo around himself, he asks Bulma for the Dragon Radar. She still has it (Turbo's Dragon Radar, if you recall), and Goku swipes it from her and rushes out of the Stadium. Muten Roshi demands him to stop, but Goku doesn't care.
His brother is dead. The only thing that can conceivably heal the overwhelming pain Goku feels is vengeance. He shouts for Kinto Un, and his loyal cloud returns to him for the first time in three years, since it had taken Goku, Upa, and the seven dragon balls to revive Bora. That time Goku sought to return life. This time he only seeks to inflict death.
Back at the Tenka-ichi Budokai Stadium, Muten Roshi is worried that Goku has gotten himself into a mess even he cannot escape from. The monster killed Kuririn, and however powerful Goku is now, after his fight with Tenshinhan he is considerably weakened. He may not live. But that's only the beginning of the old master's worries.
Oolong finds a note left by the killer, and after describing it as nothing but the symbol for "Demon", an even more shocked Muten Roshi grabs the simple letter from him. He can hardly believe what he sees. Piccolo Daimao has returned.
Lord of the Demon Clan
Many years ago, when Kame Sen'nin and Tsuru Sen'nin were young students, Piccolo Daimao and his children reigned terror over the world.
The two students were the only to survive a long and arduous battle against Piccolo Daimao's children. But they were the victors.
Until Piccolo Daimao arrived. "We had no possible way of contending with the strength of Piccolo Daimao..." Muten Roshi explains to the others, all enthralled by the master's story. "Even with Mutaito-sama's techniques we couldn't lay even a single finger on him..."
Kame Sen'nin and Tsuru Sen'nin's master.
Mutaito arrived to defend his students and defeat Piccolo Daimao in combat. Asking Piccolo Daimao why he attacks people, the Demon Lord responds, chortling maddeningly, that he wants people to see his true strength before they disappear. "As long as I live, I will not let you do as you want!" Mutaito swears.
Mutaito, quite possibly the strongest martial artist of his era, was utterly beaten by the Demon Lord. But thanks to his incredible vitality, Kame and Tsuru were able to nurse him back to health. Their master left that day, but swore to them he would return to defeat Piccolo Daimao. "I will return without fail." Tsuru Sen'nin, shaken by what had transpired, left the path of light behind, never to return. Kame Sen'nin, however, remained faithful that his master would return, and so he retreated into the mountains to train... awaiting Mutaito.
And one day, his master returned. He had trained in order to learn a secret skill said to be an ultimate technique.
"Prepare yourself! I will no longer allow you to do as you like!" Mutaito shouted at Piccolo Daimao.
He and Roshi met Piccolo Daimao once more, this time Mutaito was sure he would win.
Mutaito unleashed the Mafuba (Demon Seal), an ability designed to trap its victim in a container.
"Mutaito-sama magnificient sealed the Demon Lord inside the completely sealed Denshi Jar."
"In exchange for his own life, of course." Muten Roshi concludes. Roshi personally saw to it that the Denshi Jar (a Japanese rice cooker) was dropped to the very bottom of the ocean. Who could have released him? Who is so evil, so cunning, so dastardly that they would resort to unleashing the Demon Lord?
Surely, only one villain could be that dangerous and vile.
"I see. When all 7 balls are gathered any wish will be granted?"
Piccolo asks of Pilaf.
Pilaf assumes Piccolo Daimao will wish for world domination, but Piccolo assures him that taking over the world will not require the power of such balls. His only desire is for restored and eternal youth.
"Youth... Young and vivacious flesh that will not whither away! If I can acquire that, and that alone, I can place this world under my rule for all eternity!"
Pilaf wonders if, when Piccolo takes over the world, he can have half... after all, he did revive him from the Denshi Jar, tell him about the dragon balls, and the Tenka-ichi Budokai... or maybe a 3rd? Or... just a 4th? Piccolo Daimao tells him he'll consider it, but for now he wonders if Tambourine is back... With the Tenka-ichi Budokai roster, Piccolo Daimao can eliminate every martial artist with the potential to seal him away again.
At least, that's what Kame Sen'nin assumes.
But Tambourine is about to meet perhaps the strongest martial artist of the era.
And he won't forgive him.