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. In X2, unlike the other Light Capsules, Light does not actually describe what the upgrade is, instead showering praise to X for managing to find his capsule before beckoning him to step inside for a special surprise.

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 will not be killed by the Shoryuken if hit in his cocoon form, but instead will take as much damage as could be inflicted to make him shift to his second form. 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
In Mega Man X4, Shoryuken is one of Magma Dragoon's attacks. X can perform a similar skill by using charged Rising Fire, which can be obtained after defeating Magma Dragoon. Ryuenjin, Zero's skill counterpart to Rising Fire, is also an upward flaming attacks.

In Mega Man X5, Shoryuken is one of Spiral Pegasus' attacks. X can perform this skill to send Wing Spiral, which can obtained after defeating Spiral Pegasus.

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

Avalanche Yeti performs Hyouryuushou in a manner of Shoryuken style. After defeating him, Zero and Layer are capable of using Shoryuken as a variation of Hyouryuushou when equipped with the K Knuckle. While using Shoryuken, Zero (or Layer) performs an upward-spiraling, ice-element uppercut that freezes airborne enemies on contact.

Rockman X DiVE
Shoryuken, named "Shōryū no Hi Ken" (昇竜之火拳) in Japanese, is one of Magma Dragoon's active skills.

Rising Fire and Ryuenjin also appeared as an active skill from X (Rising Fire Ver.) and Zero.

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, Super Smash Bros. for Nintendo 3DS / Wii U, and Super Smash Bros. Ultimate.
 * Alia has unused voice lines in Mega Man X8 where she shouts "Hadouken!" and "Shoryuken!", suggesting that at one point of development, she was going to use these skills. Furthermore, unused animations for the Shoryuken as well as the Giga Crash functions that the Icarus, Hermes and Ultimate Armors use in-game were found.