Kurono Kei, a high school freshman, put on airs and thought only about girls. One day, on his way home, he came across a man who accidentally fell from the train platform. He did not care for other people, and at first he enjoyed watching the man who was about to die. However, Katou Masaru, a classmate in his elementary school days, suddenly jumped down from the platform onto the train tracks to help the man there. Being asked for help, Kei reluctantly began to help him. But when they finally got the man onto the platform, saving him, the train arrived at the station. They must have been killed by the train, but instead were instantly transferred into the room of some condominium.
There, they find a black sphere and people who are supposed to be dead like them. And there is no way out of the room. But where is this room? Why are they still alive? And what exactly is that strange sphere in the middle of the room? Kei and Masaru find out, and are horrified by the answers...