So! If you have not seen this(and if you don't want to) This game in the beginning is a visual novel dating sim. But it starts to get disturbing when your childhood friend Sayori kills herself by hanging herself. By then the game plays like she didn't exist...But the game gets a little glitchy and yuri also kills herself. They do this because of Monika, she doesn't have a role in this game. So she kills off and deletes the other characters so you can love her. But when you delete her the game starts up again with all the characters but Monika. By the end of the first day in this ending, Sayori takes the role of Monika and tries to have you all to herself. But then Monika deletes the game after saying there is no happiness in this game. And in the end she sings you a song.
If your wondering what is the wall of text up there^ I just explain what the story is about...