Associate Professor Akira Takatsuki's Conjecture Novel Volume 4 was written by Mikage Sawamura.

Spring has come for Naoya, now in his second year of college. To Professor Takatsuki's delight, Naoya signs on for another year as his assistant, and it doesn't take long for the requests to start coming in! Strange things keep happening in an architectural office, and every occurrence seems to feature the number four. A weekly magazine puts out an article about a real-life mermaid sighting! But arguably the biggest mystery of all is the appearance of a dapper British gentleman on campus… Wait, he's Takatsuki's uncle?!