"Uchū Senkan Yamato 2199: Tsuioku no Kōkai" is a two-part OVA that serves as a prequel to the "Space Battleship Yamato 2199" series. The story delves into the events leading up to the Yamato's mission to save Earth from the Gamilas threat, focusing on the backstory of key characters and the political and military tensions that set the stage for the main series.

The narrative begins with Earth under siege by the Gamilas, an alien race bombarding the planet with radioactive meteorites, rendering the surface uninhabitable. Humanity has retreated underground, but resources are dwindling, and hope is scarce. The United Nations Cosmo Navy, led by Admiral Juzo Okita, is tasked with defending Earth, but their efforts are largely ineffective against the advanced Gamilas technology. The story highlights the desperation of humanity and the sacrifices made by those in power, including Okita, who is haunted by past failures and determined to find a way to save humanity.

Central to the plot is the discovery of a message from the planet Iscandar, offering a device that can cleanse Earth's radiation. This message sparks a controversial plan to retrofit the ancient battleship Yamato into a spacefaring vessel capable of reaching Iscandar. The project is met with resistance from political factions and military leaders who view it as a futile endeavor. However, Okita and his allies, including Captain Mamoru Kodai and engineer Shiro Sanada, push forward, driven by the belief that this mission is humanity's last hope.

The OVA also explores the personal histories of key characters, particularly Kodai and his younger brother Susumu, who later becomes the protagonist of the main series. The relationship between the Kodai brothers is strained due to the death of their parents during an earlier conflict with Gamilas, and this tension is further explored as Mamoru takes on a leadership role in the Yamato project. The narrative also introduces Yuki Mori, a young officer whose determination and resilience make her a vital part of the crew.

As the Yamato nears completion, the story shifts to the political intrigue surrounding the mission. The Earth Federation is divided, with some factions willing to negotiate with Gamilas and others advocating for a more aggressive approach. This internal conflict adds complexity to the narrative, highlighting the moral and ethical dilemmas faced by those in power. The OVA concludes with the Yamato's launch, setting the stage for the events of "Space Battleship Yamato 2199."

The story is driven by its exploration of themes such as sacrifice, leadership, and the resilience of the human spirit in the face of overwhelming odds. The characters are portrayed with depth, their motivations and struggles adding emotional weight to the narrative. The OVA effectively bridges the gap between the original "Space Battleship Yamato" series and its 2012 remake, providing context and backstory that enriches the overall experience of the franchise.