Gantz, Inuyashiki Recommendations
Both anime are adaptations from manga that have been made by the same mangaka Oku, Hiroya. Both anime feature "out of this world" power that the main characters get. Similar style of weapons.
Both animes have a "trapped" feeling form the characters having to learn to adjust. Also, death goes around quite normally.
These two anime are based on manga from Hiroya Oku. You have characters in both of these anime that are affected by advanced alien technology. They also have a similar dark and disturbing feel to them seeing how they are both filled with violence, blood and gore.