Corrupted

After being devastated in the Third World War, America was divided in two. Several years after the end of the war, a crime organization called Vischio has taken control of the destroyed city of Washington, where they are holding a battle game known as KOBA (Knight Of the Bloody Alley).
KOBA is a battle game held in Washington that may result in the murder of participants. To participate, one must meet with Asmodeus and tell him their reason for their decision. Upon meeting with Asmodeus, participants are given five tags, each engraved like a card in a standard deck of playing cards. One tag must hang from the participant's neck as proof of participation. Participants must then put their lives on the line to collect others' tags, with the goal being to collect a Royal Flush. If a participant collects a Royal Flush set of tags, they earn the right to challenge "Knight" in battle. Battles end when one party either dies or lets their back touch the ground. The winner takes the loser's tags and is free to do as they please to the loser after that, often resulting in the loser's death.
The book's main characters, two young twins named Luca and Lucius, were turned into cyborgs by a mad scientist. They managed to escape and were hired for an unknown man as assassins and eventually appointed as second leaders for his organization called TAGS (Train Assist Guide Serve). One day, they were finally given another order to kill KOBA's strongest man: the Knight and find the missing members of their force.
The story follows Luca and Lucius's life in the harsh, lawless Washington as they search for the Knight and unraveled the mysteries about themselves. And before long, Luca starts to undergo change.

VERY LATE UPDATE!: I WILL NOT BE CONTINUING THIS SERIES FOR AWHILE DUE TO EXAMS AND THE OTHER BOOK!