I'm surprised by the disappointed comments because I thought the author made very clear from the beginning that only those who fight dirty wins. Right up until the end, the characters all had a choice to walk away, but the ones who still vied for vengeance end up with a "Sword of Damocles" hanging over them so of course the one who strikes first and wipes out the competition is going to win.
This mangaka does NOT right happy stories, beginning, middle, or end. He exposes the dirty side of humans in how they cling sadly, pathetically, and desperately to life and still lose in the end so I have to say that this was an amazing manga that absolutely refuses to follow norms of redeeming characters. I hated most of the characters with all their selfishness, ego centrism, and hypocrisy; going as far as even hating on the ones who are too bent on vengeance and those are not bent enough. XD
Ultimately, as abhorring as the characters were, they all fit together as amazingly well-written characters in this epic manga of a hero(ine)'s journey through a shit ton of blood, gore, and sex.