Kujo Rina is a chemistry teacher and the homeroom teacher for the 3rd grade D class at Horai High School. She doesn't have a bond with her students. On the school's graduation day, Kujo Rina is pushed from the 4th floor and falls down. She is able to glimpse a school uniform sleeve on the person that pushed her. At that time, she wonders why she was pushed and that she does not want to die. The next moment, Kujo Rina is standing in front of her students, and she has travelled back in time to one year earlier. She knows that one of the 30 students in front of her will try to kill her in a year. To find the truth about what will happen and to avoid her death, she approaches her students with all her heart. Meanwhile, Ugumori Kanau is one of Kujo Rina’s students in the 3rd grade D class. She is a model student, but she experiences a miserable school life due to her classmates targeting her.