It is now about twenty years that monsters of unknown origin, baptized as "Kaiju," arrived on Earth. Since it was discovered that the aggressiveness of these monsters could be calmed down and controlled by the voice of a young girl, the human species decided to try to cohabit with them.

The school for girls in Tatara thus proposes as a learning option the very particular profession of "trainer" of Kaijus. Ion Hidaka, a sixth grade pupil, chose to begin this unusual course. Elected at the beginning of the school year as a member of the breeding club, she must also take care every day of a gigantic monster that lives in the forest behind the school.