Rokudo Tosoki Volume 1 to 4

In a world where humanity has taken refuge underground to survive, En is a poor boy who lives off the garbage of those who are more privileged than him. He spends his days wandering the slums, searching piles of trash for the decomposing bodies of the "losers", those who were defeated and killed in the Six Kingdoms Tournament. To participate, fighters must undergo expensive body modification surgery. Recovers these modifications from the victims' bodies which significantly increase combat capabilities. Little interested in the tournament and its champion, En aspires to a simple and comfortable life. But one day, a chance encounter with a mysterious man shatters his vision of reality, and sets him on a completely different, much darker path.