Gantz, Kamisama no Iutoori 2 Recommendations
Survival games with lots and lots of deaths.
The notion of fighting for survival, where death can crop up and devour anyone who you might assume is safe. While Gantz is perhaps more gruesome with its gore, Kamisama no Iutoori Ni, offers a great story with its fair share of gruesome kills.
These are both so similar I wouldn't be surprised if one was inspired by the other. Both involve having people play a game where they must survive, people die, romances bloom. Read as they do their best to survive and overcome the mastermind which both allegedly come from outer space. They are both long giving you space to really become immersed in the story and watch relations develop, there are badass scenes and desperate times.
Both of these are dark and have similar feel to them.
They have similar main characters that are weak but grow into leaders.