Haruko is a single mother. She has an unusual living arrangement. She lives with her son Riku, her friend Aiko and Aiko's boyfriend Sorao. One day, Yuko stays at Haruko's house to attend an art institute for the summer. Yuko is the daughter of Haruko's old friend Tomoyo. They haven't spoken for many years prior to Tomoyo reaching out to Haruko to ask if her daughter could stay with her for the summer. Haruko and Tomoyo have an uncomfortable past.

Ichito Kurihara is a physician at a small hospital in Nagano Prefecture. The hospital doesn't have enough doctors, which causes Ichito Kurihara to cover many different medical fields. He is always busy. Sometimes, Ichito Kurihara is unable to sleep for 3 days due to his job. Thanks to the support of his wife Haru, Ichito Kurihara is able to carry out his work. One day, the university hospital, where he graduated from, offers a position to Ichito Kurihara. If Ichito Kurihara accepts the job offer, he will be able to spend more time with Haru and he can also learn cutting edge techniques in medicine. Ichito Kurihara also wants to keep his current patients, who were turned away from university hospitals after being told that it was too late for them.

Story continues with the students' own conflicts, Koro Sensei’s identity and the fate of the world. The time limit for assassination is approaching.

A mysterious creature destroys 70% of the moon. The creature then warns that if he is not destroyed by March of next year, Earth will be next. The creature also demands that he becomes the homeroom teacher for 3rd grade E class at Kunugigaoka Junior High School. The government is powerless to say no. The creature then becomes the homeroom teacher of 3rd grade E class which consists of failed students including Nagisa Shiota. The creature is called Teacher Koro. Meanwhile, the government requests that the students try to kill Teacher Koro even though he possesses super powers. The government offers a 10 billion yen reward for whomever successfully kills him. The students are confused by the situation, but decide to kill Teacher Koro. When their class begins with Teacher Koro, the students finds themselves having a good time with their new teacher.