In addition to the world of people, there is another - the world of monsters. This is where a nine-year-old boy finds himself, left completely alone in the middle of noisy Tokyo. In the city of monsters, Juten, a bear named Kumatetsu finds him and gives him the name Kyuta. A bizarre relationship is established between the teacher and the student: they argue with each other with or without reason. Years of hard training and adventure pass, the bonds grow stronger, and the heroes become close, like father and son... However, the world of monsters is not so simple, and the cycle of unexpected events leaves no trace of the measured way of life.