"Mobile Suit Gundam Seed C.E.73: Stargazer" is a three-episode ONA (Original Net Animation) set in the Cosmic Era timeline of the Gundam franchise. The story takes place concurrently with the events of "Mobile Suit Gundam Seed Destiny" and explores a smaller, self-contained narrative within the larger conflict between the Earth Alliance and ZAFT (Zodiac Alliance of Freedom Treaty).

The plot centers on the Deep Space Survey and Development Organization (DSSD), a neutral scientific organization dedicated to peaceful space exploration. The DSSD is developing the GSX-401FW Stargazer, a highly advanced mobile suit designed for deep-space exploration and equipped with the innovative "Voiture Lumiere" propulsion system. The Stargazer is unique in that it is powered by an artificial intelligence system, aiming to achieve autonomous exploration without human intervention.

The story introduces Selene McGriff, a DSSD researcher and pilot, and Sven Cal Bayang, a former Earth Alliance soldier turned Phantom Pain operative. Selene is deeply committed to the DSSD's mission of peaceful exploration, while Sven is disillusioned by the endless war and seeks a new purpose. Their paths cross when Phantom Pain, under orders from the Earth Alliance, attacks the DSSD to seize the Stargazer for military use. The assault forces Selene and Sven into an uneasy alliance as they attempt to protect the Stargazer and uncover its true potential.

As the conflict escalates, the Stargazer's AI begins to exhibit unexpected behavior, suggesting a level of autonomy and self-awareness that challenges the boundaries of human-machine interaction. The narrative explores themes of technological advancement, the ethics of AI, and the contrast between humanity's destructive tendencies and its capacity for exploration and discovery. The story concludes with a poignant resolution that underscores the potential for coexistence between humans and machines, even in the midst of war.

The series maintains a focused narrative, emphasizing character development and the philosophical implications of its central technology. It provides a distinct perspective within the Cosmic Era timeline, offering a quieter, more introspective counterpoint to the larger-scale conflicts depicted in "Gundam Seed Destiny."