Gantz: Perfect Answer

Kurono Kei and Kato Masaru are summoned by the mysterious black globe GANTZ. They continue the fight against extraterrestrial beings and, as they continue to battle, they become stronger. They can't escape unless they kill their enemy, the Saint. Kei opts to keep fighting to survive, but Kato Masaru hates the world which is controlled by violence and refuses to fight. As the two friends finds themselves opposing each other in a continuous game of violence, a critical last choice is to be made...