D.Gray-Man 1

Set in a fictional end of the 19th century England, the story revolves around a teenage boy named Allen Walker who is cursed with a cross mark on his hand that turns his arm into an enormous weapon, which he uses to hunt down and kill akumas. An akuma, generated by a 1,000-year-old phantom, is implanted into a human's soul during a moment of devastation and despair. The phantom uses the demons to then carry out his goal: destroy all humankind.