In the fourth episode, a disguised Korosensei sees men abusing a foreigner at a market. The woman thanks them and requests directions to Kunigigaoka Junior High. Karasuma introduces Class 3-E’s new English teacher, Irina Jelavi. The class notices Korosensei’s interest in her naked busts. Irina loved him for her thanks. Irina interrupts Korosensei’s morning lectures. Korosensei leaves for Vietnam after having Vietnamese coffee for lunch. Irina kills Korosensei in front of the students. Karma calls her Ms. Jela-Bitch because of her alienating demeanor. Irina kisses Nagisa to find his flaws, to the class’s delight. Her henchmen plot the assassination. First “lesson” with Irina is planning the assassination best fake id. Nagisa notices Korosensei’s sweet smell. Ms. Jela-Bitch teaches the class. Irina must reprimand the students for name-calling and “teach” them how to pronounce “v.” This is the “lamest lecture ever,” say students. The next day, Irina invites Korosensei to the storage shed. Karasuma’s class watches. Irina pulls Korosensei inside the shed and hides behind a curtain as machine guns fire. Korosensei is uninjured when she emerges from hiding. Erina’s lead machine gun bullets were ineffectual, and he smelled strange adult guys. He knew Irina was trapping him, so he claimed to like her. Korosensei’s punishments include a gym suit and “tentacle-doing.” Korosensei puzzles over Nagisa’s skepticism. Irina plots revenge in class. The class requests she review for midterms. Korosensei will instruct them otherwise. Irina criticizes the class for prioritizing exams over a global threat. Even if Korosensei dies, they’ll face discrimination as Class 3-E students. Irina vows to kill everyone after class riots. Irina tells Karasuma she’s an assassin, not a teacher. Karasuma at Korosensei creates individualized exams. Irina reconsiders leaving after seeing how happy Korosensei’s students are. Irina attends class. “You’re great in bed,” she writes, and students recite it. In assassinations and daily life, it’s important to be able to communicate and understand others’ languages. Irina apologizes for her rudeness. The class laughs after Irina threatens to kill them. The class called her “Bitch-sensei” to her dismay (Professor Bitch). Korosensei thinks Irina will be a good assassin. Karasuma thinks Korosensei planned this because he was a great teacher.
Koro-sensei starts episode 5 by gathering the snacks and candies students used for a chemistry experiment because he was between payments and couldn’t buy food. Okuda approached Koro-sensei with three bottles of poison after the experiment and asked him to take it. He does so without hesitation, to his face’s detriment. He asks Okuda to stay after class so they can create a poison to kill him, and she agrees, shocking her classmates. After talking with Okuda and learning why she’s in the E “As in End” Class, Koro-sensei gives her a poison formula to make at home and bring to him the next day. The “poison” turns Koro-sensei into a molten ball that can fly faster than previously. Okuda decides to use languages after he explains why they’re as important as science. Second portion of episode is school assembly. Class 3-E makes it to the auditorium, with Irina trailing behind because of the distance from their mountain to the school. Even though other youngsters taunt and dislike them, they make the best of a poor situation. 3-E’s classmates envy Karasuma and Irina. Koro-sensei stops them from pranking other pupils, shocking the upperclassmen. After the assembly, the kids rapidly file out. Nagisa stops to get a drink from the bending machine before heading back to the mountain classroom with the others. Two of his former “friends” try to make him feel terrible for having fun in class and threaten to kill him after a time. Nagisa insists they haven’t killed anyone and returns to class. The show ends while a soon-to-be-introduced character watches.
In episode 6, the students studied at the main school building. Koro-sensei turns himself into clones to teach his students (like Naruto Uzumaki, I suppose), each clone wearing a different headband to signify what each student will be learning as he teaches them one-on-one the subjects they’re poorest at (one of the students even gets a Koro-sensei clone with the Naruto headband). After that, Koro-sensei, Karasuma, and Irina see the school’s principal, Gakuh Asano, who warns him about letting 3-E students get their hopes up about increased marks and scoring well on future examinations. He even ties up Koro-sensei by throwing her a metal ring puzzle and giving her one second to finish it. Asano bids Nagisa a dry, unfeeling “good luck” before leaving for the main campus. The next day, Koro-sensei creates more clones to teach his students exam material. When the pupils ask why, Koro-sensei grows furious and takes them outside, lecturing and flattening the area around them, telling them if they don’t make the top 50, he’ll go and they’ll be trapped in this classroom forever. The students agreed to the ultimatum and fared well on the test until the 11th question, which was a curve ball to throw off Class 3-E because the rest of the school was notified of the exam adjustments. Koro-sensei apologizes, but Karma catches him off guard with a knife and reveals he made the top 50, asking whether he was afraid of being killed. Koro-sensei stays with the other pupils and continues instructing them.