Released on cellular phones in Japan, Xenosaga: Pied Piper is set one hundred 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 a.k.a. Michtam. Notable characters include Dr. Sharon Rozas, who becomes Sauer's wife and Joaquin, Sauer's stepson. His team of subordinates consists of Melisse Ortus, 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 Mikhail Ortmann, 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. Dimitri 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.
Source: Wikipedia, "Xenosaga", available under the CC-BY-SA License.