You work in a police station as usual. Another tedious day with a lot of paperwork. Suddenly, you hear your boss's voice, "Her name is Sayu, she's gonna work with you." You raise your head and see... a small girl?! That can't be true. This doesn't make any sense! How can a ten-year-old work in the police; what can she do? "Huff... Huff..." Sayu breathes softly, not looking at you. Is she sleeping?.. "Show her around," your boss says and pet Sayu's head. "Un?" she immediately wakes up.