Super Kaio-ken

The Super Kaio-ken appeared during the anime-exclusive Other World Tournament arc, which took place while Goku was deceased following his sacrifice against Cell. The tournament gathered the strongest fighters from all four quadrants of the afterlife, pitting them against each other in a martial arts competition overseen by Grand Kai.

Goku advanced through the bracket and eventually faced Pikkon in the finals, a warrior from West Kai's domain who had demonstrated the ability to defeat Cell and Frieza in Hell with minimal effort. Pikkon proved to be an incredibly formidable opponent, matching Super Saiyan Goku in both power and technique throughout their extended bout. When their battle reached a stalemate, Goku made a split-second decision to combine his Super Saiyan form with the Kaio-ken.

In one explosive instant, Goku shifted into Super Saiyan Second Grade and simultaneously activated the Kaio-ken, wrapping his golden aura in the crimson energy of King Kai's technique. The result was a momentary power spike so immense that Goku blitzed Pikkon completely, punching him into a nearby asteroid orbiting the Other World Stadium before immediately powering back down to regular Super Saiyan.

The reason Super Kaio-ken was possible at all is that Goku was already dead. King Kai had previously warned that combining the Kaio-ken with Super Saiyan was extremely dangerous because the emotional volatility of the Super Saiyan form prevents the precise ki control needed to survive the Kaio-ken's strain. Being dead removed the lethal consequences; Goku could not kill himself with the technique because he was already in Other World. Even so, the exhaustion after using it was severe.

This moment is significant in retrospect because it planted the conceptual seed for the Super Saiyan Blue Kaio-ken that would appear years later in Dragon Ball Super. The key difference is that Super Saiyan Blue provides the calm, controlled ki state that standard Super Saiyan lacks, making the combination viable for living fighters. Old Kai explicitly referenced the near-impossibility of combining regular Super Saiyan with Kaio-ken when explaining why Blue was the only transformation compatible with the technique.

Because the Other World Tournament is anime filler and does not appear in the original manga, Super Kaio-ken exists outside the main canonical timeline. However, it has been incorporated into numerous Dragon Ball video games and was given to Xeno Vegito in the Dragon Ball Heroes franchise, where it appears as "Super Saiyan Kaioken." In these game appearances, the technique has been fleshed out as a legitimate combat tool rather than the one-off desperation move it was in the anime.