Mao Natsukawa is a kind and cheerful female teacher. But at night, she is a bondage slave to vice principal Kuroda. Every night, tied up, Mao gasps in emptiness. The trigger for this was two years ago, when her student Minase was found to be working a part-time job and smoking without permission, and was forced to drop out of school. Mao happens to meet Minase again...