X-Buster

The X-Buster (エックスバスター) is Mega Man X's primary weapon in all games from the Mega Man X series. It is the Mega Buster Mark 17 created by Dr. Light alongside X. X can transform any of his arms into a powerful arm cannon to attack, and has an energy amplifier that allows it to be charged up and release a more powerful shot.

The X-Buster also has a Variable Weapon System that allows X to use the Special Weapons of Reploids defeated by him, and it can also be powered up with different Armor Parts and Power-Up Parts. In The Day of Sigma, it's shown that X can detach his buster.

In Mega Man X: Command Mission, the X Buster was redesigned alongside X, and it is his starting weapon. X can find better versions of the X Buster during the game, the X Buster MKII and X Buster MKIII. X can also equip different types of busters. His Action Trigger is a Charge Shot.

Appearances in other games
In the Mega Man Zero series, the X-Buster is one of the Ten Shining Weapons. As X only appears as a Cyber-elf in the series, his buster isn't show, but his copy, Copy X, also has a buster.

In Mega Man ZX, a X Buster is Vent/Aile's primary weapon when using the Biometal Model X.

The X Buster also appears in the first Mega Man Legends game as an item that can be used to create the powerful Shining Laser. Its description says it is a laser weapon with batteries not included.

Rockman X manga
The X-Buster is near identical to the games, but originally it is only available in X's left arm. X can use Special Weapons by inserting chips from defeated enemy Reploids in his buster. During the battle against Sting Chameleon, his buster is severely damaged, but Armored Armadillo ordered a Metall C-15 to repair it, disobeying Sigma's orders to have a honorable one-on-one combat against X. Late in the story, X's buster is damaged again in the battle against Boomer Kuwanger in a tower, and it becomes useless when he takes an energy cable from the tower and attaches it to his buster to fire a giant blast that destroyed Kuwanger and part of the tower. Without ways to attack, he is in disadvantage against Vile, but Zero gives his buster to X, allowing him to battle.

In the Rockman X2 manga, X gains the ability to use his buster in any arm, but he can use only one of them at a time. However, when facing the three X-Hunters in their base, he uses both busters at the same time to defeat them.