The students the distract Koro with an embarrassing video of him. Due to his distraction, he didn’t notice that the chapel had been lowered and at high tide, Koro is slowed down due the water.
The elaborate plan of the students drives Koro into a corner and he is nearly destroyed. However, apparently Koro can regenerate. Also, he can shrink his body down and harden it around himself. The crystal makes him unable to move for an entire day until the crystal dissolves.
Despite getting further than even the worlds’ armies, the students are all discouraged. After heading back and having something to drink, all of the students that get sick. An artificial virus was used to make the students ill and a proposition is made. Another marksman infected them and has the antidote. Karasuma is told to send Kaede and Nagisa (the two shortest) to the hotel atop the mountain and hand over Koro-sensei in his current form.
They are only given an hour to hand over Koro. However, together Koro and Ritsu come up with a plan for the healthy students to sneak into the hotel and steal the antivirus. With that, the episode ends and I am left saying ‘wtf’ over and over. I don’t think I ever expected Assassination Classroom to get this intense, haha.
My favorite part of this week’s episode would have to be when Karma began to torture Koro-sensei in his crystalized form by placing an embarrassing picture of Koro in front of him and putting a slug on him.