Unlockable Items
Axl's White Armor:
Beat the game and have all of Axl's metals, then beat the last boss with a double attack using Axl.

Zero's Black Armor:
Successfully beat the game and have all Zero's metals purchased.

Zero's Sigma-Blade:
Successfully beat the game and use the cleared save and the Sigma-Blade can be bought at the lab.
X's Ultimate Armor:
Successfully beat the game with all of X's metals and all 8 pieces of armor.

Endings:
To see one of the three different endings get the final hit on the boss with Axl, X, or Zero.