It is extremely unusual for a female to be born with two unique souls: one of a human and the other of a kaiju. These exceptional people, termed "Kaiju Girls," had the appearance of a regular human but the uncanny skills of a huge monster. GIRLS, or the International Kaiju Rescue and Mentoring Organization, was founded to assist these Kaiju Girls in adjusting to their talents and finding a place in civilization. Three young females have recently awoken their kaiju half. The spirit of Agira is inherited by the introverted Aki Miyashita, Windom is inherited by the serious Reika Shiragane, and Miclas is inherited by the effervescent Miku Ushimaru. They all join the organization GIRLS, where they learn how to control their terrible inclinations and exploit their talents. Thanks to the assistance of those around them, Agira, Windom, and Miclas each discover what it truly means to be a Kaiju Girl.