
Root Letter (stylized as √Letter) is a visual novel adventure game developed and published by Kadokawa Games, serving as the inaugural title in their Kadokawa Game Mystery line. In the story, players must uncover the truth behind Aya's disappearance, a girl who vanished under mysterious circumstances after receiving a specific letter. The game features two distinct gameplay styles: an investigative segment where players interview individuals who knew Aya to gather clues, and a simulation mode where players re-experience and interact with past events involving her.
| PS4 | June 16, 2016 |
| Vita | June 16, 2016 |
| PC | July 7, 2017 |

| Audio | Subtitles | Interface | |
|---|---|---|---|
| 繁體中文 | ✓ | ✓ | |
| English (US) | ✓ | ✓ | |
| 日本語 | ✓ | ✓ | ✓ |