Root Letter (stylized √Letter) is a visual novel adventure video game that is developed and published by Kadokawa Games as the first title in their Kadokawa Game Mystery brand. In the game, the player must figure out what happened to the character of Aya, a girl who mysteriously vanished after receiving a particular letter. The gameplay will be split into two distinct parts; the adventure part, where the player interrogates characters who knew Aya in order to find more information about her, and the simulation parts, where the player relives and plays through prior interactions with Aya.