Zombie Chronicle

When the zombie apocalypse breaks out, he binds to the Obsession Tag System—every special zombie he kills grants him a fragment of a life. A firefighter's arms, a teacher's ruler, a mother's last breath... Others use tags to stack stats, but he uses them to stack memories. As all of humanity turns into monsters, he alone carries the tombstones of a city, living on for the dead. — Description from novelcodex.org