The Occult Club was created by Reita (which he created in an attempt to pick up chicks) but the only other people who joined were Kusuo (forced to join), Shun, Chiyo (who was just following Kaidou), and a spooky girl named Arisu.
Since Reita's plan didn’t work, he decided to give up on it. At some point he ended up changing it to make Kusuo the club president. Kusuo later finds out that Chiyo and Arisu have been the only ones showing up for club since then. The club is located in the audio-visual room.