Final Fantasy X-3: Rise of the Shadows

A fan fiction on Fanfiction.net that takes place 18 years after Final Fantasy X-2, and follows the story of Tidus and Yuna's oldest daughter, Simone, who is chosen to stop an ancient evil that threatens to destroy Spira. Spira has entered an era called the Eternal Calm, technology has quickly advanced over the years and the population of Spira is growing at a very fast rate. Everything seems peaceful until strange beings known as Shadows invade Besaid one night, and from then on, things would never be the same again.