Zero the Ghost Detective had the ability to summon the dead as well as interact with them on a physical level, as such he was able to defend the innocent from malevolent spirits.
As his adventures never lasted more than 5 pages no details such as a back story, how he got his abilities or even a real name were ever revealed.
Usually Zero did not demonstrate any real magical abilities, though he was the master of many magical artifacts. Zero described himself as an "ally" with death, which gave him powers to battle the supernatural undead. He dispelled ghosts with a mere gesture, and caught glimpses of the future.