Selene

Umbra, nicknamed Aki by Ventus, is a young girl sealed within the deepest parts of Castle Oblivion, imprisoned in a frozen casing until Ventus woke from his own slumber and freed her by accident. At the same time, this also led to the release of Erebus, the True Darkness to the world.

Trivia

 * While her original name Umbra is Latin for darkness, her nickname Aki is written with the characters for second (亜) and hope (希).