The eighth installment of the spin-off Koro-Sensei Quest! turns a treasure hunt into chaos when E Class and Korosensei open an empty legendary chest that swaps everyone's bodies, carrying each person's bug along. A rescue team battles Kunudon to find a cure, though Korosensei ends up trapped in a Kunudon's form.
Deep inside a mysterious cavern, E Class hunts for a fabled treasure chest said to hold the key to beating the Demon King. Nagisa and Karma pop it open only to find it empty, but a burst of light reveals its true trick: it swaps everyone's bodies around. Panic and confusion follow, with the group scrambling to manage their unfamiliar new forms and discovering that each person's personal bug transferred along with the switch.
A rescue team sets out through the cavern to hunt for a cure, battling Kunudon along the way and stumbling through the trouble their borrowed bodies cause. Repeated bug mishaps knock a wash bin loose and open a hidden door, while the pervert-prone members have to be restrained to keep them from misusing their swapped bodies. The team eventually locates a magical egg that restores everyone to normal, with one exception: Korosensei and a Kunudon trade places, sending the creature fleeing and Korosensei chasing after it to reclaim his own body. Amid the celebration, the class forgets Tadaomi, still left tied to the ceiling.
An empty legendary chest unleashes a body-swapping effect on Class E and Korosensei. Each character's Koro Sensei Quest bug carries over into their new body during the switch. The rescue party fights through Kunudon and triggers a concealed door via a repeated bug. A magical egg reverses the swap for everyone but Korosensei, who ends up trapped in a Kunudon's body and gives chase to fix it.
The episode is part of the comedic spin-off series Koro-Sensei Quest!, using the opening theme Re:QUEST! and the ending Seishun Satsubatsuron Remix. It first aired in Japan on February 9, 2017, followed by its English broadcast on February 16, 2017. It sits between the entries The Big Five Attack! and Showdown at Fukuma Tower.

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Yes, Big Bad Switcheroo is the eighth episode of the comedic spin-off series Koro-Sensei Quest!. The spin-off follows Class 3-E and Korosensei through a fantasy-style treasure hunt adventure.
In Big Bad Switcheroo, Class 3-E and Korosensei discover a legendary chest during a cavern treasure hunt that turns out to be empty, but it swaps everyone's bodies around. The class scrambles to manage their unfamiliar new forms while each person's personal bug transfers along with the swap.
A rescue team locates a magical egg that restores everyone to their own body, with one exception. Korosensei ends up trapped inside a Kunudon's body and has to chase after the creature to reclaim his own form.
Big Bad Switcheroo first aired in Japan on February 9, 2017, with its English broadcast following on February 16, 2017. It sits between the episodes The Big Five Attack! and Showdown at Fukuma Tower in the Koro-Sensei Quest! spin-off.
By the end of Big Bad Switcheroo, amid the celebration of reversing the body swap, the class forgets that Tadaomi Karasuma is still left tied to the ceiling.
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