Trouble Succubus "Darling, Kon'ya Mo I~ppai Ecchi Shichao"

Toshiyuki is a uni student. He temporarily lives alone since his parents are abroad on business. One day, while enjoying lunch time together with Rie, his neighbor, a cute girl suddenly appears in front of them. "Ah, you're my darling. Let's make a baby now!" The girl, Nina, tells him that she is from the devil world, and he is appointed to become the next devil king. He doesn't know what's happening, but they start having sex anytime, anywhere. What will happen to them in the end...?