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 in 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 Mega Man 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 uppercut, 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. 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 by defeating him, Rising Fire (charged) and Ryuenjin, are upward flaming attacks similar to the Shoryuken.

Shoryuken is also one of The Skiver's attacks.

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

Shouryuuken is also the technique Zero and Layer obtain after defeating Avalanche Yeti. With the K Knuckle equipped, Zero performs an upward-spiraling, ice-element uppercut that freezes air-borne enemies upon contact.

Street Fighter X Mega Man
Shoryuken is used by Ryu.

Trivia

 * Mega Man's Mega Upper attack from Mega Man 2: The Power Fighters and Super Smash Bros. for Nintendo 3DS / Wii U is similar to the Shoryuken.