Ok, I'll add my epilogue.
After they came back from the trip, and Akiko got relieved from her duties as Emperor, Misono and her fucked so long and hard their movements went back in time and they are now know as the Great Earthquake.
The end.
There literally has never been a good manga with the premise of "classroom game where students have to kill each other/or die one by one". Between this and Ousama game I can't decide which one is worse.