Big Bad Switcheroo (episode)

Big Bad Switcheroo is the eight episode of Koro-Sensei Quest!

Overview
Class E and Korosensei have found a weird item-fetching quest when a strange force unexpectedly swaps around their bodies and minds.

Summary
E Class has arrived to find a legendary treasure chest in a mysterious cave. Nagisa and Karma open the chest which supposedly contains something to defeat the Demon King. However, instead it emits a bright light and proves empty. The students are dumbfounded before realizing it does have an effect... to switch people's bodies. Everyone is disconcerted and bewildered over the change, and "Taiga" ties up "Megu" to prevent him from acting pervertedly with her body". "Karma" and "Kaede" look on, feeling bad for Megu. "Tōka" is excited at having a large chest for once, while "Tadaomi" takes the opportunity to act pervertedly with "Irina" and tries to take off his clothes. They also discover each other's bugs are transferred along with the change, though "Isogai" is stuck with only half a suit of armour.

"Tadaomi" and "Megu" are both tied to the ceiling to prevent them from being perverts with their new bodies. "Korosensei", "Irina", "Nagisa", "Itona", "Rinka" and "Ryūnosuke" go off to search for way to turn everyone back to normal. While fighting the Kunudon's blocking their way, "Itona" takes care of the with his speed but slips and hurts himself, being unused to having normal limbs. "Nagisa" repeatedly activates his bug, causing a wash bin to fall and open a mysterious door.

After worrying if "Megu" is still alive, the students release him, only for him to immediately start misbehaving. "Karma" starts to worry that something happened to his body, and goes to search for them. "Toka", "Yuma" and the others go after them. "Karma" asks what happened to "Nagisa" but is told to avert his eyes. He looks, only to find "Nagisa" dressed in a bikini, mocking "Karma" that despite it being girl's only armour, he can wear it. They later find a magical egg and turn everyone back to normal... except for Korosensei and a Kunudon, who switch bodies. The Kunudon then runs away, with Korosensei chasing them to get his body back.

Meanwhile, the class has forgotten about Tadaomi, who is still tied to the ceiling.