Ep. 18: Students face a virus threat while Koro-sensei remains trapped in an indestructible crystal sphere.
Students attempt to assassinate Koro-sensei by showing him a movie that exposes his embarrassing habits, weakening his mental state. This distraction allows them to shoot off his tentacles, which had bloated due to water filling the chapel, and trap him in a hydraulic cage. Koro-sensei then activates his ultimate defense, encasing himself in an indestructible crystal sphere for 24 hours, rendering him invincible but immobilized. The class laments their failure until several students fall ill from a deadly virus spiked in their drinks by a mysterious third party. This antagonist demands the immobilized Koro-sensei in exchange for the antidote. Refusing the trade, Koro-sensei and Ritsu devise a plan to infiltrate a high-security hotel to retrieve the cure themselves.
Episodes
- Ep. 14 · Koro-sensei's pool weakness exploited by Terasaka's failed assassination attempt
- Ep. 15 · Koro-sensei offers tentacle shooting as prize for top exam scores in end-of-term finals
- Ep. 16 · Class 3-E and 3-A compete in exams, earning tentacles and an Okinawa resort wager.
- Ep. 17 · Hinano and Taiga prepare while Lovro trains students for the island assassination mission.
- Ep. 18 · Students face a virus threat while Koro-sensei remains trapped in an indestructible crystal sphere.
- Ep. 19 · Karasuma and Irina infiltrate a guarded hotel while facing Smog and Grip
- Ep. 20 · Karma Evades Gas Attack While Nagisa Disguises as Girl to Clear Path to VIP Floor
- Ep. 21 · Koro-sensei uses nicknames to confuse Gastro while Takaoka reveals his plan involving Kayano and the antidote.
- Ep. 22 · Terasaka intervenes as Nagisa overcomes Takaoka using Lovro's technique and a stun-gun.