The Occult Research Club was a group Izuko Gaen, Meme Oshino, Deishuu Kaiki, Yozuru Kagenui, and Tadatsuru Teori were a part of in college. The members studied oddities and the supernatural, though they also played a lot of shogi. Most of them supposedly shared majors.
They were also responsible for the resurrection and creation of the tsukugami who is now known as Yotsugi Ononoki. Most members have since become oddity specialists.
In the novel, Kagenui recalled Oshino and Gaen being the only members who took the club seriously. The club played so much shogi to the point they forgot to recruit new members. When they finished college, Kagenui thought the club went under and she was the only one who graduated while Oshino and Kaiki dropped out.