In a certain school, there exists a bloody history: 10 years ago, several students were brutally and mysteriously murdered. Rumor has it that it was the work of the "Book of Demise," a collection of urban legends and tall tales. Inside this book, it is said that the "Bookmark of Demise" turns the page it rests on into reality. 
 
Four rumor-loving friends—A-ya, an antisocial boy who relishes starting such rumors; B-ko, a popular girl who acts polite around others; C-ta, a level-headed boy who is A-ya's childhood friend; and D-ne, a quiet and introverted girl—at this school have discovered how to acquire the Book of Demise. Performing the ritual, they become part of the Demise Game—but realize too late that they are in over their heads. 
 
To escape this game, they must weed out a traitor among them. However, at the same time, the Bookmark of Demise is turning urban legend to reality, revealing an eerie connection to the events of 10 years ago and creating a living nightmare of lies and betrayal. (Source: MAL Rewrite)

Due to a single traitor, the game has begun. Those that wish to escape must abide by the terms and reach the end. Now, let this fun Demise Game begin― 
 One-Man Hide and Seek, Doppelgangers, Mearry-san's Messages, Monkey's Hand .... A group of four boys and girls become involved with a certain game though the "Bookmark of Demise," a taboo that is said to have been brought back from ten years prior. Carry out the "demand" written in the mysterious letter, and perform the urban legends. Otherwise, you will die.