You are a death row convict on a mission to retrieve "the elixir of life" which grants a person immortality if consumed. You alongside 12 other convicts have been sent on this mission with the promise of a full pardon to whoever successfully delivers the elixir, but only one person can receive this pardon. However the island it is located on, Shinsenkyo which is filled with mystical monsters and beings that humans have no experience fighting.