Zero Buster

The Zero Buster (ゼロバスター) and Z-Buster (ゼットバスター) are Zero's main long range weapons in the Mega Man X series.

Zero Buster
In the first three games, Zero uses the Zero Buster, a chargeable arm cannon embedded in Zero's arm(s) that is more powerful than the X-Buster, in Mega Man X being able do damage Vile's Ride Armor while X couldn't. If X didn't obtained the Arm Parts from the First Armor after defeating Vile in Sigma's hideout, Zero will give his arm cannon to X.

In Mega Man X2 and Mega Man X3 the Zero Buster(s) can be charged to use the Hyper Zero Blaster (ハイパーゼロブラスター), allowing Zero to fire two Charge Shots one after the other from each; however, they do not combine. In Mega Man X3, the Zero Buster has four charge levels:

When Zero became a fully playable character in Mega Man X4, his buster was completely removed due to game balancing.

The Zero Buster is also used by Zero in Marvel vs. Capcom 3.

Z-Buster
The Z-Buster is introduced in Mega Man X5; in this game, it is only usable if the game was started with Zero, as he loses it in his battle against Sigma Head if starting with X. However, the usage of this buster was stripped down drastically. It can only be used on the ground, and Zero is unable to move while firing it because he has to "charge" the attack.

When Zero was resurrected in Mega Man X6, the Z-Buster received new abilities. The fire frequency of the Z-Buster was vastly increased (yet still bound to the ground) and its power was increased as well, making it rather useful against most enemies and bosses. After Mega Man X6, the Z-Buster was never used again in the series.

Other media
In the Rockman X manga series, Zero's buster is his primary weapon until his death in the end of Rockman X. When he revived in the end of Rockman X2, he mainly uses his beam saber, but still uses his buster at times. After Sigma's defeat in the Rockman X3 manga, Zero's buster malfunctions during a mission and becomes unusable, and it was destroyed when he used Earth Crush in another mission.

Trivia

 * In the Mega Man Zero series the Z-Buster was replaced by the Buster Shot gun, which Zero took from the deceased Milan to protect Ciel. The Buster Shot was mistranslated as "Z Buster" in the first Mega Man Zero game, a mistake that was fixed in Mega Man Zero Collection.