Season 1 of Eternal Yesterday premiered on October 21, 2022.

Koichi is cheerful and popular in the class. Mitsuru is talented and not good at socializing. The two high school students are strongly attracted to each other due to their opposite personalities. However, one morning, Koichi is hit by a truck in front of Mitsuru. Koichi got up on the spot and smiled as usual, and although he was indeed "alive", his classmates gradually began to forget about Koichi's existence.