Twelve years ago, an incident known as "Blast Fall" unleashed major destruction and chaos. Now, years have passed, and mankind has learned to adapt by incorporating cybernetic limbs into its citizens. Roy Revent is a bounty hunter known for his violent acts towards criminals due to the loss of his daughter in Blast Fall; and when a criminal tries to take revenge on Roy, an unknown girl falls from the sky and saves him. She has no memory of who she is, or where she came from. With the help of Miranda, his boss and landlord, he takes in the girl and gives her a name of Solty. What is the real identity of Solty, and what caused Blast Fall?