"Kaijū Girls ~Ultra Kaijū Gijinka Keikaku~" is a 12-episode anime series that reimagines the classic Ultra Series kaijū (monsters) as anthropomorphic, humanoid girls. The story is set in a world where kaijū have been transformed into "Kaijū Girls," beings who retain some of their original monstrous traits while taking on human forms. These girls are tasked with protecting Earth from a mysterious threat known as the Space Kaijū, who seek to invade and destroy the planet.

The protagonist, Red King, is a former kaijū who has been reborn as a Kaijū Girl. She is joined by other Kaijū Girls, including Eleking, Gomora, and Pigmon, each representing a different kaijū from the Ultra Series. Together, they form the Kaijū Defense Force, an organization dedicated to combating the Space Kaijū and safeguarding humanity. The series explores their efforts to adapt to their new lives, balance their human and kaijū identities, and work as a team to face increasingly dangerous foes.

Throughout the series, the Kaijū Girls encounter various challenges, both external and internal. They must confront their own insecurities and pasts while learning to trust one another. The narrative also delves into the origins of the Space Kaijū, revealing a deeper connection to the Kaijū Girls themselves. As the story progresses, the stakes escalate, culminating in a climactic battle that tests the strength and unity of the Kaijū Defense Force.

The series blends action, comedy, and lighthearted moments with occasional emotional depth, particularly in its exploration of identity and teamwork. While primarily episodic in structure, it builds toward a cohesive resolution, tying together the characters' personal growth with the overarching conflict against the Space Kaijū. The Kaijū Girls' unique abilities and personalities drive the narrative, offering a fresh take on the kaijū genre while paying homage to its roots in the Ultra Series.