The Power of Kaio-Ken! Goku vs. Vegeta! (これが界王拳だ！！限界バトルの悟空ＶＳべジータ Kore ga Kaiōken da!! Genkai Batoru no Gokū tai Bejīta) is the thirteenth overall episode in the Dragon Ball Z Kai series. The episode first aired on June 28, 2009. Its original American air date was June 8, 2010. Its Dragon Ball Z counterparts are "Lesson Number One" and "Goku vs. Vegeta".
With Vegeta ready to enter the fight, Nappa realizes that he has lost, and prepares to attack Gohan and Krillin. Not fast enough to stop the Saiyan brute, Goku unleashes the Kaio-ken technique. Using his new Kaio-ken Finish technique, he paralyzes Nappa. With his partner now useless, Vegeta mercilessly kills Nappa. Goku tells Gohan and Krillin to leave so he can fight Vegeta without any distractions.
After moving to a new battleground, Gizard Wasteland, the last two Saiyans begin their epic battle. The two seem evenly matched for a short time, sparring. However, Vegeta powers up, and Goku is getting badly beating using the regular Kaio-Ken. Realizing the horrible dilemma, Goku prepares the Kaio-Ken x2. Goku managed to have increased his power, but is not enough. Goku soon realizes that even the 2x Kaio-ken isn't enough to defeat his opponent. He then decides to break his promise to King Kai and use the 3x Kaio-ken. Struggling to get his power increase to use, the episode ends with Goku about to attack Vegeta with his new power boost. Will it be enough?