Fate/Zero

The Fourth Holy Grail War has begun, and seven mages must summon heroes from history to battle each other to the death. Only one mage-and-hero pair will remain to claim the Grail and have their wishes granted! Kiritsugu Emiya was once an assassin but now fights in this war to save the world from those who would destroy it with the Grail’s power.

(Source: Dark Horse)