The Ar tonelico series is set in a planet called Ar Ciel. At some point in its history, its land mass was lost in a catastrophe caused by humans.
It's a science fiction fantasy game. There are these genetically engineered / artifical humans called "Reyvateils" that use singing to control machinery and the giant tower that serves as the central structure to the remaining, levitating, land mass which is the only place where humans can live anymore.