Upon entering high school, Natsumi Asami is told an utterly unbelievable story by all her other classmates during the first homeroom on the day of the entrance ceremony. "So, everyone in this class except me, including the teacher, has been repeating the same year, year after year, for 12 years?" Thus began Natsumi's high school life—a delightful and enjoyable daily life, surrounded by classmates who seemed to have come to a realization.

—Until March 31st, one year later, until that day's end.

※This is the serialized version of the short story "The Case of the Classmates Who Had Been Looping for 12 Years Entering Sage Mode."