Keyblade Armor

Armour is armor that protects the Keyblade Wielder from Darkness when traveling to other worlds. The Armour obeys their Keyblade Wielder just like the Keyblade.

Kingdom Hearts Birth by Sleep
Terra, Ventus, and Aqua all use Armour when they travel to other worlds. When Terra is possessed by Master Xehanort in Keyblade Graveyard, Terra's Armour come to life to become the Lingering Sentiment and defeat Xehanort. When Aqua fights Xehanort in Radiant Garden, he unlocks his own heart and is engulfed by darkness. When Aqua and Terra/Xehanort are about to fall into darkness together, she commands her Armour to save Terra/Xehanort from swallowing by the darkness.

Kingdom Hearts II Final Mix
Aqua's Armour appeared in Chamber of Repose and was shown talking to Xemnas. Lingering Sentiment fought Sora in the Keyblade Graveyard.