The Ashura Senkuu (阿修羅閃空, lit. Asura/Fighting Demon Flashing Air) is a special teleportation attack used by Akuma, as well as some of his other counterparts who mimic his fighting style (such as a variation by his brother Gouken). He glides backward or forward depending on the command while on a focused zen-state one-legged stance.
It grants him invunerability until the move is complete, but he cannot attack during it, making it a typical teleport. It can be used for escape and mindgames, though later games have had the move made easier to counter, especially due to its predictable startup and ending of momentum at the end of the move, where the user is bound to be vunerable.
Akuma and other characters tend to use this technique's animation for their dashing animation in many of the Vs. games.