Doubt, Torikago no Tsugai Recommendations
A gathering goes horribly wrong! Torikago no Tsugai's students meeting up to search for a missing person, or Doubt's players of a social game deciding to see each other offline - the tables turn when everyone is forced to play a very real and deadly game! The moment you stop concentrating on the game, you're very likely to turn into dead meat. A psychological, mentally challenging setting of dread kindly reminds the players to avoid just that. Their goal is to find the one pulling the strings behind the game... If they can survive, that is!
There is a recurring theme of birds in Torikago and
Both manga deal with high school students suddenly finding themselves in a life and death situation, wherein manipulation, lying and double crossing become the norm. Both have a sense of mystery to it, because there is obviously someone who deliberately put them into the situation that they are right now. It also has little to no character development, alongside an info dump towards the end that wraps up the mystery, with ZERO foreshadowing.
The bad guy is the one who is least likely to be suspected, thus easily becoming the #1 suspect (if you have half a brain to recognize said suspect, that is)