"Mobile Suit Gundam Silhouette Formula 91" is a manga series set in the Universal Century timeline, focusing on the development and deployment of advanced mobile suits during a period of political and military tension. The story centers on the Silhouette Formula Project, a secret initiative by the Earth Federation Forces to create next-generation mobile suits capable of surpassing existing models. The project aims to counter the growing threat posed by the remnants of the Principality of Zeon and other factions seeking to destabilize the Federation.

The protagonist, Shuu Kajima, is a skilled mobile suit pilot and test pilot for the Silhouette Formula Project. Tasked with piloting the experimental F91 Gundam, Shuu becomes a key figure in the Federation's efforts to maintain control. The F91 Gundam, equipped with advanced technology such as the Bio-Computer system and VSBR (Variable Speed Beam Rifle), represents a significant leap in mobile suit design. However, its development is fraught with challenges, including technical limitations and political interference.

As the story progresses, Shuu and his allies face off against various adversaries, including rogue Zeon forces and rival factions within the Federation. The conflict escalates as the F91 Gundam is tested in real combat scenarios, revealing both its strengths and vulnerabilities. The narrative explores themes of technological advancement, the ethical implications of warfare, and the personal struggles of those caught in the crossfire.

Supporting characters include Annamarie Bourget, a fellow pilot and Shuu's close ally, and Dorel Ronah, a high-ranking Federation officer with ambiguous motives. The interactions between these characters add depth to the story, highlighting the complexities of loyalty, ambition, and survival in a war-torn world. The manga also delves into the broader political landscape, depicting the Federation's internal divisions and the lingering influence of Zeon's ideology.

The plot is driven by a series of intense battles, strategic maneuvers, and personal confrontations, culminating in a climactic showdown that tests the limits of the F91 Gundam and its pilot. Throughout the series, the focus remains on the interplay between human ingenuity and the destructive potential of advanced technology, offering a nuanced portrayal of the Universal Century's ongoing conflicts.