Shoryuken

Shoryuken (昇龍拳;) is a special move from the Street Fighter series that appeared in some Mega Man games, mainly in the Mega Man X series.

Mega Man X2, Mega Man Xtreme and Mega Man Xtreme 2
Mega Man X can learn the Shoryuken by entering the game's secret capsule. In Mega Man X2 it is executed with →↓↘+ATTACK while X is at full health and on the ground. In the two Xtreme games it is executed by charging the X-Buster and holding ↑ before releasing the attack. X will surround his arm with fire and perform a powerful jumping uppercut in a spiraling recovery motion, causing massive damage to its targets.

While it is believed to kill all bosses in one hit, it does not. If the edge of the boss is grazed, it takes heavy damage, but does not kill it entirely. Morph Moth and Wire Sponge will not be killed by the Shoryuken if hit in their first forms, but instead will take as much damage as could be inflicted to make them shift to their second forms. Sigma's viral form takes several hits to be killed with the Shoryuken. (although it's possible to one-shot Sigma by trapping him on the ceiling)

The Shoryuken is not saved in passwords.

Mega Man X4 and Mega Man X5
Shoryuken is one of Magma Dragoon's attacks. The abilities obtained after defeating him, Rising Fire (charged) and Ryuenjin, are upward flaming attacks similar to the Shoryuken.

Shoryuken is also one of Spiral Pegasus' attacks.

Mega Man X8
The Shoryuken is one of the techniques X can perform when using the Ultimate Armor.

Shoryuken is also the technique Zero and Layer learn after defeating Avalanche Yeti. With the K Knuckle equipped, Zero performs an upward-spiraling, ice-element uppercut that freezes airborne enemies on contact.

Street Fighter X Mega Man
Shoryuken is used by Ryu.

Other appearances
As a move used by Street Fighter characters like Ryu, Ken, Akuma, and Sakura, the Shoryuken is present in many games where they appear alongside Mega Man characters, such as Marvel vs. Capcom, Marvel vs. Capcom 2, Marvel vs. Capcom 3, SNK vs. Capcom: SVC Chaos, Tatsunoko vs. Capcom, Namco × Capcom, Project X Zone, and Super Smash Bros. for Nintendo 3DS / Wii U. The move is also used in the Archie Comics crossover Worlds Unite. In Marvel vs. Capcom: Infinite, X remarks that he had always wanted to see a real Shoryuken when fighting against Ryu.

Trivia

 * The original Mega Man performs a similar uppercut named Mega Upper in Mega Man 2: The Power Fighters, Marvel vs. Capcom, Marvel vs. Capcom 2, and Super Smash Bros. for Nintendo 3DS / Wii U.