Lately, there's been a cute black cat that lingers in front of Kouta Kawamura's door. But one day, he comes home to see that the cat is no longer around, but a pretty boy dressed in black is there instead. Curious and captivated by his face, Kawamura decides to let the boy into his house.The boy has no name, but he seems to care about Kawamura deeply. In return for letting him inside and taking care of him, he decides to pay him back "with his body". Unable to refuse, Kawamura ends up having sex with him, and decides to call him "Kuro". This is the story of their unique cohabitation.