有三个朋友从高中开始就在一起，但2013年，其中一人去世。这两个还活着的人正慢慢地试图忘记他最好的朋友的去世，并过上平静的生活。然而，在2018年，其中一位朋友收到了他最好的朋友的一封电子邮件，他在五年前去世，并指责他忘记了这封邮件。在那里，奇怪的事件发生在他的随行人员中，为了试图结束这一事件，他将在高中时与他们一起上课的Shiori的帮助下，寻求发现朋友死亡背后的真相。

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.