Karasuma visits Pope Gakuhō Asano, who devises a plan to lure Koro-sensei into a trap. Koro-sensei and the students of Class 3-E go into the Ruins of Tribulation with three chambers hosted by a Guardian Kunudon.

The students have a new addition to their class, her being the Autonomous Intelligence Magic Stone Tablet, who can perform various forms of sorcery.

Itona Horibe the Silver Berserker crashes through the classroom, and his guardian Mage Shiro tells Koro-sensei that Itona will be the new Demon King.

lass 3-E talks about Class 3-A's Big Five (Gakushū Asano, Teppei Araki, Ren Sakakibara, Natsuhiko Koyama and Tomoya Seo), an elite group of paladins.

Class 3-E finds a treasure chest deep in a cave, but it turned out to be empty when it is opened. To make matters worse, everyone switches bodies with someone else.

The female students go to Irina to brew a potion for sacks of chocolates. On Valentine's Day, some of the female students give some of the male students the sacks of chocolates, but it turns the male students into monsters for a day.