Associate Professor Akira Takatsuki's Conjecture, Vol. 7 (light novel)

A female Seiwa student comes to Professor Takatsuki and Naoya looking for advice. She tells them about going with her club friends to a building where the elevator supposedly transports whoever rides it to another world, and the next day, one of their group vanished without a trace.

Next, the pair receive a request from afar and head deep into the mountains of Tochigi. They find themselves in the middle of a construction site where mysterious events continue to occur as the builders t…