Aqua (Japanese: アクア Hepburn: Akua), also known as Master Aqua (マスター・アクア Masutā Akua), is a fictional character from Square Enix's video game franchise Kingdom Hearts. Having first made cameo appearances in Kingdom Hearts II, Aqua is one of the three protagonists who is introduced in the prequel Kingdom Hearts Birth by Sleep. She is one of the Keyblade apprentices training under Master Eraqus alongside Terra and Ventus. As Eraqus' friend Master Xehanort leaves, Aqua and Terra are assigned to find him and defeat the Unversed.