The story of Ar Tonelico (a series of games) is set on the world of Ar Ciel, a planet orbited by the moons Viola and Cello. It is a world ravaged by disasters (the most significant of which were man-made) where comparitively few creatures yet live. On this world exist three mechanical towers that stand high above all else on this planet and it is on these structures which the last of this world's living creatures depend. The towers are ancient relics of a bygone civilization capable of high technology so powerful that it literally destroyed itself during the catastrophic incident known as the Grathnode Inferia - an incident brought about by war, hatred, and greed. This was an incident which destroyed all natural land and shrouded it an endless ocean of poisonous gas known as the Sea of Death also covering the entire sky with an ocean of plasma which destroys everything that touches it.
Humans and creatures known as Reyvateil (artificial life forms created by men using the now lost art of Sound Science) dwell in civilizations held aloft by the power of the three towers. These are civilizations maintained in no small part by Reyvateil, due to their ability to link with and influence the massive mechanical structures as well as their ability to influence the world with the power of their Song Magic. It is a tense existence humans live with Reyvateil, one prone to conflict and ever threatened by the fragility of their unnatural environments. A tragic existence which still somehow manages to be liveable… most of the time.