1000 words can't explain how terrible this is. If you want to keep your sanity just stay away from this. If you're a "M" then please feel free to watch it. I have watch all 12 episodes I can say this. Everything about this game doesn't make any sense at all, literally EVERYTHING. From the backstory about what causing all of this to how it all end up here to the character itself, even the game itself broke its own rule.
Look if you don't care about the story and just want to see a bunch of highschooler killing each other while (sometimes doing adult stuff), this anime will satisfy you.