Insanity (狂気, Kyōki) is the 5th episode of Muhyo & Roji's Bureau of Supernatural Investigation anime series.
Muhyo has taken care of the spirit that infects people through touch, but Roji feels he's to blame for the chaos it caused and takes off alone. Yoichi follows him and tells him a story from when he and Muhyo were attending the Magic Law School together - a sad story about the two of them and their friend Enchu, a kind, earnest boy who was working harder than anyone to become an executor.
Yoichi tells Roji about their school days with Enchu. One day they were late for class and as punishment the teacher gave them difficult problem, but Enchu was able to solve it. Enchu was focusing studying and wanting to become executor in order to be able to financially support his mother. He tells Muhyo to study too, but Muhyo shows no interest, but as an evil spirit attacks them, Enchu panics, while Muhyo manages to easily stop the spirit using the Magical Law pen. As Enchu and Muhyo are the top students, an exam is coming that will determine which one will become an executor. Enchu takes it seriously and is studying all day and night, while Muhyo takes it easy. On the day of the exam, Enchu receives news that his mother was in critical condition and he rushes back home. As he returns to school, due to missing the exam, Muhyo was chosen as executor. Since that day, Enchu changes and tries to destroy the Association, Muhyo and the rest of the executors.
Nana gives the burning piece with Muhyo image to him and sees the man she saw standing on a rooftop. Muhyo sees that's Enchu and greets him. Enchu then teleports into their room and greets him back and then releases vengeful spirits across the whole Association and then disappears. The spirits starts to scream and kill people with it. Yoichi fights and defeats some of them and instructs Roji to go find Muhyo. Roji thinks Yoichi will be more helpful, but Yoichi explains that Muhyo chose him and even if he wanted to be the assistant of Muhyo, there must be a reason why Muhyo wanted Roji. Getting his confidence back, Roji rushes to Muhyo and manages to come in time and defeat the spirits. The original body of the vengeful spirit shows up being Enchu's shirt. Muhyo explains that Enchu sealed some wandering spirits in his shirt so that he can call them anytime. Muhyo gets his book back and punishes the spirit with Hell Train. The train comes out of the ground and takes the spirit along with the rest of the scattered spirits back to Hell.
Muhyo asks Roji if he can endure Enchu's attacks, as he won't stop until either Muhyo is back or Muhyo manages to drag him out of the dark side. Roji starts to believe Muhyo means they will part ways, but Muhyo explains that he needs to be closer to him as he no longer can guarantee his safety. Hearing that Roji is relieved. As the trains return to Hell, Muhyo falls asleep from exhaustion. Yoichi tells Roji its unfortunate that the exam got postponed, but Roji is fine with it as he learned a lot about Muhyo. Yoichi then shows him a temporary first-class license for his efforts and jokes with Roji that he doesn't need it then. Seeing it, Roji starts chasing him wanting to take the license.