Gantz

Hiroya Oku's Gantz is brutal, juvenile, and hard to put down. A teenager named Kei Kurono dies in a subway accident and wakes in a Tokyo apartment with a black sphere called Gantz, which equips him and other recent dead with sci-fi gear and orders them to kill aliens hiding among the living. Survive enough missions and you might earn your life back. The manga is notorious for its graphic violence, its cynicism about how people behave under pressure, and its very early use of digital 3D rendering for the monsters and cityscapes. It is not subtle, but it is relentless, and it captures something ugly and true about panic and self-interest.