This episode shows a little back story on Fujiko's brother and the school. In the past, Fujiko's brother was asked by a blonde-haired guy to do a mission involving the placing of three artefacts around the school in order to seal off something powerful, and left her a message to deliver a hint to Fujiko when his task was complete. After completing this task he realized the man didn't want to destroy the new Maou, but he wanted his power, so the blonde man killed him in response.
Back in the present, Akuto is having trouble controlling his powers, so it is suggested he place himself in solitary confinement in the Mental Self-Discipline Chamber for 12 hours in order to reflect on his special power. During that time, it cannot be opened from the inside, so Fujiko hatches another plan to use that to her advantage by preparing a hallucinogenic agent and emptying it inside the chamber, thinking that once Akuto goes crazy, he will run to her for salvation. She flashes back to the time where she remembered her brother lying in a coffin, accused of being a coward, and suddenly his responsibilities fell on her shoulders.
Sai finally decides to go into the chamber with Korone acting as her official "observer" position dictates. However, to his surprise, Kena Soga snuck in with them in her invisible form before the doors closed, so now she gets stuck as well. Akuto sighs and leans back, only to accidentally uncover a treasure map that someone left behind.
Unfortunately, she also forgot to pee before she became locked in the chamber, causing everyone to go crazy as they try to find a way out of it. On the other hand, when Fujiko arrives to inject her special gas, she thinks that Akuto is already suffering from his solitary confinement and hits the emergency release button on the outside. Instead of Sai, she gets knocked over by Kena making a mad dash for the bathroom, but in her haste she drops the treasure map and Fujiko picks it up, recognizing her brother's handwriting.
The next day, copies of the treasure map are being pasted all around school. Akuto and Fujiko each think the other's responsible, when Korone points off to show Kena happily pasting more copies of the map on the walls. The day after that, some students return with blood on their bodies, having tried to find the treasure and being attacked for it. The student council President Lily Shirashi tells Akuto to make a speech about it, but when he does, everyone thinks that he's behind the map and the attacks as well.
All of a sudden, a green haired girl latches onto his head with her long legs, daring him to venture down into the labyrinth mentioned on the map if he didn't plant the map himself. She reveals her name to be Eiko Teruya, then leaves.
The day after that, Lily offers to let him fake going into the ruins marked on the map, but Akuto feels the need to see the danger for himself anyway. Fujiko lets him borrow her special gun (in pill form) before he leaves. When he gets ready for the trek, Hiroshi has packed some camping gear and teams up with Korone. However, Eiko pops up out of nowhere and decides to tag along as well. Hiroshi feels a bit jealous as the four of them prepare to enter the labyrinth.