There are three friends who have been together since high school, but in 2013, one of them died. The two people who are still alive are slowly trying to forget the death of his best friend and live their lives smoothly. However, in 2018 One of the friends receives an email from his best friend who died five years ago and accuses him of having forgotten it. From there, strange events take place in his entourage and to try to end it, he will seek to discover the truth behind the death of his friend with the help of Shiori who was with them in class in high school.