A mysterious and beautiful young woman with a hypnotic singing voice named Ai finds herself waking up lost on the cold, hard streets of Tokyo with no memory of who she is or why she's there. She must go on a journey to search for her identity and salvation in this world and beyond. She must piece together clues about who she is, why she's on earth, and the secret of the seemingly deadly heart-shaped box she carries. (Source: MAL)