Released on mobile phones in Japan, Xenosaga: Pied Piper is set 100 years prior to the start of Episode I. It explores the past of the cyborg character Ziggy when he was a human named Jan Sauer and working for the Galaxy Federation's counter-terrorism task force.
The events take place on planet Abraxas (aka Michtam). Notable characters include Sharon Rosas, who becomes Sauer's wife; and Joaquin, Sauer's stepson. His team of subordinates consists of Meris Orthas, who witnesses Jan Sauers's suicide and later founds Scientia; Lactis, an early model Realian equipped with "Canaan"; Erich Weber or as later discovered, Voyager; and Michael Oltman, an experienced U.M.N. operator.
The purpose of Xenosaga: Pied Piper is to develop the back stories of some of the most important yet rarely felt presences in the Xenosaga universe, including Ziggy, chaos, Wilhelm, Voyager and Dr. Dmitri Yuriev. The plot itself spans three chapters. It centers on Sauer and his team as they track a serial killer known only by the hacker alias "Voyager", who kills his victims using the U.M.N. network. The game was also Soraya Saga's final contribution to the Xenosaga project. A translation script can be found at http://zarathustra.kaisho.org/