Manga Life Game

"I want you to play a game. You don't have a choice in the matter. I will come for you soon" was written in a letter received by high school student Hitotsubashi Seiya who immediately threw it to the bin as a bad joke! How little did he know, soon after he found himself waking up in a sealed room with a bunch of strangers... all asking the same questions... where are they? Why are they there? And more importantly how will they get out?!