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

A FAMILY AFFAIR.Takatsuki's estranged cousin Yuuto reaches out for the first time in decades. Apparently, a growth has appeared on his fiancée's shoulder -- and it's taking the shape of a face! The moment he and Naoya meet her, she addresses Takatsuki as “Tengu-sama” … Then, on their web page, they receive a request from someone who lives at a traditional Japanese inn. The client is a nineteen-year-old girl who claims that when she was a child, her mother was sucked into a mirror… Will the supernatural wonders never cease?