"Kaiju Girls" is a short-form anime series that blends comedy, action, and science fiction, set in a world where kaiju—giant monsters—are a central element of society. The story revolves around three high school girls—Black King, Red King, and Miclas—who are reincarnations of classic kaiju from the Ultraman franchise. These girls attend Kaiju Girls Academy, a school designed to train kaiju-human hybrids to protect Earth from extraterrestrial threats. Each girl embodies the traits and abilities of their kaiju counterparts, with Black King being calm and composed, Red King fiery and impulsive, and Miclas cheerful and energetic.

The narrative begins with the girls adjusting to their new lives as kaiju-human hybrids, learning to control their powers and work together as a team. Their peaceful school life is disrupted when alien invaders, known as the Baltan, threaten Earth. The Baltan, who also have ties to the Ultraman universe, seek to conquer the planet, forcing the girls to confront their fears and embrace their kaiju heritage. As the series progresses, the girls face various challenges, both in battle and in their personal lives, as they strive to balance their human emotions with their kaiju instincts.

Throughout the series, the girls encounter other kaiju-human hybrids, some of whom become allies, while others pose new threats. The story explores themes of identity, teamwork, and the struggle to reconcile dual natures. The girls' growth is marked by their increasing ability to harness their powers and work cohesively, culminating in a climactic battle against the Baltan. The series maintains a lighthearted tone, with comedic moments and slice-of-life elements interspersed with action-packed sequences, making it an accessible and entertaining watch for fans of kaiju and Ultraman lore.