Associate Professor Akira Takatsuki's Conjecture, Vol. 6 (light novel) — Mikage Sawamura

Takatsuki's estranged cousin Hiroto reaches out to him. Apparently, a growth has appeared on his fiance's shoulder -- and it's taking the shape of a face! But the moment they meet her, she yells "Master Tengu" and runs over...! Then, on the website they use to collect stories, they receive a request from someone who lives in a traditional Japanese inn. The client is a 19 year old girl, and she claims that when she was a child, her mother was sucked into a mirror... Will wonders never cease?