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, it is able to damage Vile's Ride Armor while the X-Buster couldn't. If X does not obtain the Arm Parts from the First Armor, before defeating Vile in Sigma's hideout, Zero will give his arm cannon to X.

When Zero is revived in Mega Man X2, the design of his buster changed alongside him. Zero uses his buster in his fight against X if they battle. When X is at an intermediate distance, Zero fires a small charged shot. If X is at a further distance, Zero will fire two large charged shots one after the other (one from each arm) followed by a shockwave from his beam saber. This triple attack is used by Zero to destroy his copy if X recovers all of Zero's body parts from the X-Hunters.

In Mega Man X3, the Zero Buster can be charged to use the Hyper Zero Blaster (ハイパーゼロブラスター) attack. Zero can fire two charged shots, one after the other (one from each arm); however, they do not combine. 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.

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, since he loses it in his battle against Sigma Head if starting with X. However, the usage of this buster was rather unfavorable since its power was stripped down drastically (in comparison to Zero Buster in the previous games). It can only be used on the ground and Zero is unable to move while firing it, because he has to "charge" the attack. He can only attack with his Lv.1 charged shot. His Lv.2 charged shots only appear during his fight as a boss.

Awakened Zero uses a special attack from his Z-Buster during his fight as a boss known as Shingetsurin (『真月輪』, "True Moon Ring"), replacing his standard pair of Lv. 2 shots. Zero shoots two blue ring-like projectiles that home in on X wherever he's moving and after a moment, they will home in on X one more time to try and hit him again.

When Zero was resurrected in Mega Man X6, the Z-Buster received new abilities. The firing frequency of the Z-Buster was vastly increased (yet still bound to ground-only usage) and its power was increased as well, making it rather useful against most enemies and bosses.

Zero Nightmare uses a special barrage attack from his Z-Buster during his fight as a boss. After doing his standard combo of shooting a pair of Lv. 2 shots and launching an energy wave from his Z-Saber, he'll fire an onslaught of Lv. 2 shots. Zero Nightmare begins to use this technique when his health is low.

After Mega Man X6, the Z-Buster was never used again in the series.

Fighting games
The Zero Buster is also used by Zero in Tatsunoko vs. Capcom: Ultimate All-Stars and Marvel vs. Capcom 3 in the form of either his throw attacks (forward throw involves him jamming his firing buster at his foe, while his back throw is a nod to his Tensou Shot/Transfer Shot in SNK vs. Capcom: SVC Chaos where he dashes past and fires at his opponent's back), or his Hyper Zero Blaster move, indicating that it is a technique with the buster rather than the buster attack itself. Like the Mega Buster itself used by the two Mega Men in the past Vs. Capcom games, Zero can walk around while charging it and it can also be fired in midair (while firing it on a downward angle), though Zero will drop the charge if he gets hit. It is very useful in terms of extending combos, to cancel into other special attacks and to put pressure to the opponent from afar. It becomes more faster when it is fully charged and can pierce the opponent for 3 hits. The colors of his charged shots are based on the charges from Mega Man X3 in Tatsunoko vs. Capcom, while in Marvel vs. Capcom 3 instead they take ever previous shots done in the past games: Lv1. is based on his shots from Mega Man X5 and X6; Lv.2 is based on his shots from Mega Man X2 and X3 and his Lv.3 is based on his shot from Mega Man X2, since it is notably the most yellow. The buster charge takes around 6 seconds to fully charge in Tatsunoko vs. Capcom, while in Marvel vs. Capcom 3 it has been buffed to 3 seconds, and the shot is slightly bigger. In the Ultimate version of Marvel vs. Capcom 3, Zero can now charge his Hyper Zero Blaster during the start of a round, and the knockdown properties of the attack have been nerfed. Also, the firing part of the attack can now be cancelled into from his special moves, increasing Zero's zoning potential.

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

Trivia

 * Zero's original buster has the same appearance as the Arm Parts from X's First Armor. When his buster's appearance was redesigned by Serges in Mega Man X2, it should be interesting to notice that this design was only used in that game, since his buster's design from Mega Man X3 is the one kept for the rest of the series and became its trademark look for other media appearances. Also, if one looks very closely to his sprites from Mega Man X3, all will notice that it looks the same from his Mega Man X2 sprites, despite the change according to artworks.
 * The existence of Zero's Buster would be completely ignored through the entirety of Mega Man X4, appearing neither in gameplay or flashbacks. Mega Man X5 retroactively rewrote his Buster back into the story, showcasing its use during his battle with Sigma during Zero's Maverick state originally shown in X4.
 * In Zero's list of attacks from Mega Man X2, in Compendium of Rockman X, the Zero Buster is named Z-Buster.
 * 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.