Super Kaio-ken (超界王拳 Chō Kaiōken, lit. "Super World King Fist" or "Super Fist of the King of Worlds"), also called Super Saiyan: Kaio-ken, is a combination of the Super Saiyan transformation and the Kaio-ken technique.
Goku uses this technique while fighting in the Other World Tournament against Pikkon. By using the power of Kaio-ken while in his Super Saiyan form, Goku gains a massive power increase, which is statistically equivalent to that of a Super Saiyan 2, by taking the 2x multiplier of these forms into consideration. Goku is seen punching Pikkon towards an asteroid orbiting the Other World Stadium, after which he reverts to his Super Saiyan form.
It was mentioned by Old Kai in Dragon Ball Super it is stated that using Kaio-ken alongside Super Saiyan is almost impossible or rather lethal, because the intense emotional turmoil caused by the Super Saiyan transformation would not allow precise ki Control to survive the technique. This may be why Goku has only used Super Kaio-ken while deceased.
Video game appearances
In the Dragon Ball Z arcade game by Banpresto, Goku has the Kaio-ken as one of his special moves, and he is able to use it even in his Super Saiyan form. Similarly, in Super Dragon Ball Z, Goku is able to use Super Kaio-ken by transforming into a Super Saiyan, and then using Kaio-ken.
In the Dragon Ball Z Collectible Card Game, Goku can use this Kaio-ken in combination with any of his appearing Super Saiyan forms: Super Saiyan, 2nd Grade Super Saiyan, Super Saiyan 2, Super Saiyan 3, Golden Great Ape, and Super Saiyan 4.
In Jump Super Stars, Goku can oddly use this in his Battle Koma 5 as his Special B/Up Special, being able to use it as a charged attack which increases the amount of physical blows he will perform in the brief combo for that one attack. It is used in the same fashion as the Super Kaio-ken (due to BK5 Goku being in Super Saiyan mode by default), only Goku simply has the red aura's outline with no actual change to his colors inside of said aura. It has been somewhat rectified in Jump Ultimate Stars, with Goku having his Battle Koma 5 being in his normal form instead.
In Dragon Ball Xenoverse 2, while the it is impossible to use the Kaio-ken and Super Saiyan Awoken Skills together, though it is possible to used Kaio-ken-based Super and Ultimate Skills such as Kaioken Assault, Kaioken Kamehameha, and its x4 and x20 Ultimate Skill variations along with any of the Super Saiyan forms available to the Saiyan Future Warrior (including Super Saiyan 2 and Super Saiyan 3). While the Kaio-ken aura is visible when these attacks are used, it does not grant any increase, thus the Future Warrior only visually appears to be using the Super Kaio-ken. It should also be noted it is possible to uses these skills with other Awoken Skill transformations such as Potential Unleashed or the Frieza Race's Turn Golden form, as well as the Kaio-ken Awoken Skill itself.
The technique made its official video game debut in Dragon Ball Z: Dokkan Battle where Goku is a playable character in this form.
Xeno Vegito as Super Saiyan can use the Kaio-ken technique in Super Dragon Ball Heroes.