"Urikupen Kyūjotai" is a science fiction anime series set in a futuristic world where humanity faces an existential threat from mysterious alien entities known as the "Urikupen." These beings, characterized by their amorphous, gelatinous forms, possess the ability to absorb and assimilate organic matter, rendering them nearly invulnerable to conventional weapons. The story centers on the efforts of a specialized military unit, the Kyūjotai, tasked with combating the Urikupen and protecting the remnants of human civilization.

The narrative begins with the sudden emergence of the Urikupen, which rapidly overrun major cities and devastate global infrastructure. In response, the Kyūjotai is formed, comprising elite soldiers equipped with advanced technology and experimental weaponry designed to counter the Urikupen's unique properties. The unit is led by Commander Akira Tachibana, a seasoned strategist with a personal vendetta against the aliens, and includes a diverse cast of characters such as Rei Nakamura, a brilliant but emotionally distant scientist; Haruto Saito, a hot-headed pilot with exceptional combat skills; and Yumi Fujimoto, a compassionate medic who struggles with the moral implications of their mission.

As the series progresses, the Kyūjotai engages in a series of high-stakes battles against the Urikupen, uncovering the aliens' origins and motivations. The Urikupen are revealed to be the result of a failed human experiment in bioengineering, created to solve environmental crises but ultimately evolving beyond control. This revelation forces the characters to confront the ethical dilemmas of their own actions and the consequences of humanity's hubris.

The plot is driven by the Kyūjotai's efforts to develop a countermeasure capable of neutralizing the Urikupen threat. This involves infiltrating heavily guarded alien strongholds, deciphering cryptic data left by the experiment's creators, and navigating internal conflicts within the unit. The series explores themes of survival, sacrifice, and the blurred line between humanity and monstrosity, as the characters grapple with their own humanity in the face of overwhelming odds.

Key narrative arcs include the discovery of a Urikupen hive mind, which poses a new level of threat, and the introduction of a rogue faction within the Kyūjotai that seeks to exploit the aliens for their own gain. The climax of the series involves a final, desperate assault on the Urikupen's central core, where the fate of humanity hangs in the balance. The resolution ties together the personal journeys of the main characters, offering a mix of triumph and tragedy as they confront the consequences of their choices.