Deadman Wonderland: Akai Knife Tsukai

Two years after the catastrophic tidal wave that swept over Japan, police officer Kiyomasa Senji is trying to make the world a safer place. Using his Branch of Sin powers, he stops criminals in whatever ways he can. After rescuing a boy named Izuru Tsukiyoshi from a gang called Goreless Peace, the conflict between Kiyomasa and his adversaries heats up rapidly, to the point of being explosive.

Offering a glimpse into the past of the future Deadman, the story follows Senji, helping to further develop the reasoning that drives his actions later in life.

(Source: MAL Rewrite)