Zombie Powder Vol 1:

Zombie Powder Vol 1 By: Tite Kubo Art by: Tite Kubo
Non-fiction: Manga, Western-Action, 189 pages
Book Count: 24

This manga is by the same person that does Bleach, it also uses the term Shinigami in the first 30 pages.  In this world a collection of 12 Rings of the Dead create something called zombie powder that is said to be able to bring the dead back to life and grant immortality onto the living.  Gamma is a man collecting the rings. He is also a man that has a metal hand that he uses to stop bullets with as they are being fired, brings a sword to a gun fight and wins, and has a partner who is honestly trying to kill him.  When he gets his "wallet" stolen by Elwood, a boy who is working with a gang to save money to help his sickly sister, their lives get interwoven.  The gang shoot Elwood's sister to get the reward money on Gamma's head and Elwood vows to help find all the rings to bring his sister back.