Aqua is a character from the upcoming game Kingdom Hearts: Birth によって Sleep.

While Aqua's name means 'water' in Latin, Kairi's name means 'sea' in Japanese. Any connection between the two is unconfirmed, however similar name meanings also apply with Sora and Ven, and with Riku and Terra.

Kingdom Hearts II Filmatics

She first appears as a young, blue-haired female knight who fights alongside Ven and Terra in the secret ending movie of Kingdom Hearts II: Final Mix+. She is the first to be unmasked when her ヘルメット gets smashed after being thrown to the ground in battle. She and Ven briefly take on...