In a society where humans and beastmen coexist. Guest, a professional dog trainer, is asked to take in and train a single "dog" rescued from a kennel that suffered a massive hoarding collapse. An adult dog of unknown breed—that was the information provided beforehand. However, the individual brought to Guest was a tattered young man, a canine beastman.

Lacking even basic social skills, let much less the ability to eat or use the bathroom properly, Guest gives him the name "Nero" and begins his training.