"Mobile Suit Gundam Seed C.E.73: Delta Astray" is a manga series set in the Cosmic Era timeline of the Gundam franchise, serving as a side story to the events of "Mobile Suit Gundam SEED Destiny." The narrative centers on the exploits of the Junk Guild, a group of scavengers and engineers, and their involvement in the ongoing conflict between the Earth Alliance, ZAFT, and other factions. The story primarily follows Jess Rabble, a skilled mobile suit pilot and member of the Junk Guild, who becomes entangled in a series of escalating battles and political intrigues.

The plot begins with the Junk Guild recovering a heavily damaged mobile suit, the Delta Astray, from a battlefield. This unique machine, equipped with advanced technology and a mysterious AI system, becomes a focal point of the story. As Jess pilots the Delta Astray, he encounters various factions vying for control of the suit and its capabilities. Among these factions is the Librarian Works, a shadowy organization seeking to manipulate the war for its own ends. The Librarian Works deploys its own advanced mobile suits, including the Hyperion Gundam, to challenge Jess and the Junk Guild.

Throughout the series, Jess and his allies navigate a complex web of alliances and betrayals. The Junk Guild, while neutral in the broader conflict, is repeatedly drawn into skirmishes as they attempt to protect their independence and the Delta Astray. The narrative explores themes of technological advancement, the ethics of warfare, and the impact of conflict on individuals and societies. Key characters include Jess Rabble, whose piloting skills and resourcefulness drive much of the action, and Canard Pars, a former ZAFT soldier with a personal vendetta that intersects with the Junk Guild's missions.

The manga also delves into the broader political landscape of the Cosmic Era, highlighting the tensions between Coordinators and Naturals, as well as the machinations of various military and corporate entities. The Delta Astray itself becomes a symbol of resistance and innovation, embodying the Junk Guild's ethos of repurposing and survival in a war-torn world. The series concludes with a climactic battle that underscores the high stakes of the conflict and the enduring resilience of its protagonists.