The Great Ghost Plan

It's a hot day and Zorori, Ishishi, and Noshishi want to cool off. Suddenly a storm comes and gravestones appear out of nowhere. Ghosts appear and terrify the trio until they find out the ghosts are Youkai-sensei's students. Youkai explains that they are old ghosts who have lost their self-confidence. Zorori agrees to help them out but only after Youkai sways him with a reward for his troubles. They set up a haunted house and wait for someone to pass by. After a day of waiting an elementary school class passes by. Zorori has one of the ghosts conjure up a storm to get them to stay at the house. Surely scaring a bunch of kids will be easy, right? Based on book 17.