Seiei Enbu

Seiei Enbu (星影円舞) is a special weapon from Street Fighter X Mega Man. When used, Mega Man will move faster, jump higher and will generate afterimages after he moves, also, when Mega Man uses his buster, the afterimage will shoot as well. Making it a great weapon for bosses. However, once activated, Mega Man will not be able to switch weapons or stop the use of the weapon, consuming 1 energy per 2 seconds. Although, when charging his buster, the weapon consuption is paused until the charged shot is released. This weapon is applied to Mega Man's default Mega Buster weapon, so it's technically another special weapon that can be selected and used. The weapon can be used by pressing the left Weapon Change button and the Fire button at the same time.

The only way to obtain this weapon is by the use of a secret code:

On the Start Screen, hold down the Fire and Jump Buttons for 6 seconds until a noise can be heard, indicating the activation of the code. This code also unlocks the original Hadoken.

Trivia

 * The Sei'ei Enbu is Yang's special attack in the Street Fighter series.
 * During the development of the game, Yang was originally planned as a boss character but was ultimately replaced by Chun-Li. But the coding for his weapon was left in the game and was later used as a secret code feature.