Our protagonist, Shinbou Takeru, grew up in a single-parent household. When his father remarried, he had a beautiful new family: his stepmother Hitomi and stepsister Tsukasa. However, in the midst of this happiness, his father sadly passed away in an accident, leaving his family behind. Ken and his family continued to live their lives as an ordinary family. But, a few months ago, something terrible happened to his stepmother's and stepsister's bodies. They were not pregnant, yet their breasts were gushing with breast milk! What's more is that if they didn't pump it regularly, it would interfere with their daily lives. But for some reason, they couldn't pump it themselves and it could only be done by those of the opposite sex. So Ken ended up having to help milk his stepmother and stepsister, but even though they were family... he couldn't contain his arousal after rubbing their big breasts day in and day out...