Xenosaga is primarily a series of science fiction video games developed by Monolith Soft and published by Namco. Xenosaga's main story is in the form of a trilogy of PlayStation 2 video games. Several side stories and spinoff projects have also been developed, as well as an anime adaptation.
The Xenosaga series serves as a spiritual successor to the game Xenogears, which was released in 1998 for the PlayStation by Square (now Square Enix). These two works have links through allusions, stylistic connections, and design similarities. The creator of both Xenogears and Xenosaga is Tetsuya Takahashi, who left Squaresoft in 1998 along with Hirohide Sugiura. Using funds from Namco, they started Monolith Soft and the Xenosaga project.
The first game in the primary trilogy, Episode I: Der Wille zur Macht ("The will to power" in German), was released in February 2002 in the Japanese market, and then in February 2003 in the American market. Xenosaga Freaks, a lighthearted game with a playable demo for Episode II was released in April 2004 in Japan, but was not released elsewhere. Episode II: Jenseits von Gut und Böse ("Beyond Good & Evil") was released in June 2004 in Japan and February 2005 in North America. Xenosaga: The Animation, an anime based on Episode I, premiered on TV Asahi in Japan on January 5, 2005. Xenosaga: Pied Piper, a three chapter-long cellphone-based game depicting the history of cyborg "Ziggurat 8" 100 years before the start of Episode I, was released in Japan in July 2004. Pied Piper was not released in the United States. Released on July 6, 2006, Episode III: Also sprach Zarathustra ("Thus spoke Zarathustra") is the final title in the Xenosaga series, effectively cutting the initial projection of the series in half (see section). A retelling of the first two episodes (titled Xenosaga I & II) was released on the Nintendo DS in March 2006 in Japan.
All three episodes of the main Xenosaga trilogy are named after the books of Friedrich Wilhelm Nietzsche. The first episode is named after The Will to Power, a book published posthumously by his sister Elisabeth Förster-Nietzsche. Several Nietzschean concepts and references appear throughout the series.