"Charge ahead while firing a Kamehameha behind you!"
Reverse Kamehameha (逆かめはめ波) is a propellant variation of the Kamehameha.
The user fires a Kamehameha directly at the ground, propelling them up through the air in a jet-like manner. The technique is mainly used as a way to change directions quickly, remain airborne longer, or to fly through the air quickly, all of which apply for non-fliers.
Master Roshi uses the technique as Jackie Chun during his match against Krillin at the 21st World Martial Arts Tournament. Goku uses a Reverse Kamehameha while in a submarine with Bulma and Krillin to escape the Pirate Cave falling on them, which propels the submarine all the way out of the cave and the ocean. He later uses the Reverse Kamehameha during his match against Tien Shinhan in the 22nd World Martial Arts Tournament. He uses it later in the final battle against King Piccolo to perform the Penetrate! technique. Later, in the 23nd World Martial Arts Tournament, Goku uses it to enter into the mouth of Piccolo, and after to escape of Piccolo's Chasing Bullet.
Goku also uses the technique to try get out of Hell and back to the Snake Way. Krillin uses a similar technique to try to distract Nappa during a team attack performed by he, Piccolo and Gohan. Goku also uses the technique when his Capsule Corporation spaceship gets in the gravitational pull of the Alpha H-Z star while heading to Namek, which allows him to escape a fiery doom. He uses it again during his battle against Frieza on Namek. Goten uses it in the form of a hand-stand during his match against Trunks in the 25th World Martial Arts Tournament while using the Assault! rush.
Goku uses the Reverse Kamehameha again in an underwater cave on Gelbo, near Zoonama's lair. Later, he uses the technique as propulsion between the Deserted Spaceship and the Grand Tour spaceship in space.
Appearances in games
The technique was named Reverse Kamehameha in Dragon Ball Z: Super Gokuden: Totsugeki-Hen. It is called Reversed Kamehameha (逆カメハメ波) in Dragon Ball: Daimaō Fukkatsu. The Reverse Kamehameha is also used by Kid Goku and Krillin in the Butōden series, and when Kid Goku uses the Penetrate! in the Budokai series and Budokai Tenkaichi series.
This technique is called Kamehameha Boost in Dragon Ball Xenoverse and is one of Goku's Super Skills. It is also one of the Future Warrior's obtainable skills through the GT Pack 1 DLC. Via the DLC it can be purchased at the Skill Shop or obtained in DLC Parallel Quest Event: "Small But Strong!".
In Dragon Ball Xenoverse 2, the Kamehameha Boost returns as a Super Skill used by Goku which the Future Warrior (Xenoverse 2) can obtain by purchasing it from the Skill Shop in Conton City for 4,500 Zeni after defeating both the Masked Saiyan and Masked Future Warrior in the main story.