Threads of Destiny (Japanese: 赤い糸, Hepburn: Akai Ito, lit. "Red Thread") is a 2006 cell phone novel series written by Mei. Akai Ito was first published on the website Mahō no Toshōkan, where it became the #1 ranked story within the first month of publication. The popularity of Akai Ito has been associated with the boom of cell phone novels in the mid-2000s in Japan. The novel was later published as a series of five books, which sold a consecutive total of 1.8 million physical copies.

The success of Akai Ito has led to a manga adaptation by Cocco Kashiwaya, a television and film project released under the title Threads of Destiny, and two video game adaptations.