The Z fighters are all still in pursuit of Supreme West Kai. As they are flying, Vegeta begins to vomit and makes a landing. Behind some rocks, Vegeta vomits up what looks like some parasitic worm. Right before his eyes, the worm grows larger in size and begins the develop what looked to be arms and legs. All Vegeta could do was stare, not only because he had been weakened by his sickness, but also because of his fear of worms.
The worm then formed into the form of a man who somewhat resembled Raditz, then flew off.
The worm man landed in a playground for children and after observing how terrified a little girl was of a bee, he mutated his hair to match it's black and yellow pattern, believing he would strike fear into the hearts of the humans. The man vaporized the children and their parents, finding joy in the deaths of others.
He then flys off again and meets Supreme West Kai. She explains that he is her child, a Saiyan-Kai hybrid. She names him Rigor and instructs him to kill Goku and the others. Rigor however defects her orders and kills Supreme West Kai by decapitating her with an energy beam.
After laughing at his good work, Rigor becomes curious about the Z Fighters Supreme West Kai told him about. He flew off in search of them and found they were all looking for West Kai. Rigor proudly states what he had done to her and offers to do the same to all the Z Fighters. Goku goes ssj5 and fights Rigor briefly before being injured.
Rigor decides to kill them all for being so weak and fires a planet- crushing blast directly at the Z fighters. Vegeta arrives just in time to deflect the blast and recommends to Goku that they fuse to beat him just like they did to beat Xicor.
The two preform the fusion dance (Kibitoshin Kai took away the potara earrings) and became ssj4 Gogeta.
Rigor fought with Gogeta for a little bit, but clearly had the upper hand. Before long Gogeta had received the worst beating he had ever had.
Rigor was beginning to become , he hadn't killed anything for the past half hour, and fired his signiture attack, Death Torrent, and Gogeta and the others. Knowing he had to stop Rigor within the little time he had left in his fusion Gogeta countered with a full power Big Bang Kamehameha. Even at full power, Gogeta was losing the battle between the two super attacks colliding, but he wouldn't give up, even though his fusion may wear off at any moment.
Rigor laughed the whole time as Gogeta struggled. But suddenly he felt a sharp pain in his chest. Rigor was never taught how to control his power, which surpassed even Xicor's, and now his body began to shut down on him. Gogeta's Big Bang Kamehameha took a large advantage over Rigor's failing attack, and it swallowed the Saiyan-Kai Hybrid up.
After the dust settled and all the Z fighters began to celebrate their victory, Rigor reappeared from under the rubble, shocking everyone.
Believing it was better to die and take everything with him rather than admitting defeat, Rigor maximized his power and blew himself up, similar to how Vegeta tried to destroy Fat Buu all those years ago.
Gogeta, knowing he had only seconds left to his fusion, contained Rigor's blast before it could destroy too much of anything. Afterwards the two split from their fused form. Master Roshi estimated that if Gogeta hadn't contained Rigor's blast, the entire solar system could have been engulfed.
About a month later, King Kai told Goku that in 10 years time, a new threat would emerge and that the Z fighters would need to spend every second of it training for its arrival.
