- Visit Madotsuki's and Urotsuki's room in the Chess Board at least once.
- Turn the chess board black by either triggering it randomly by stepping on a tile or passing through a pair of columns.
- Go between the two queens in the north area where the reference room used to be.
- Make sure no effect is in use and interact with the mask behind the giant spike that has replaced the room.
- Follow the path into a room that appears to be Usotsuki's room. Take the book on the desk to aquire the effect.