Kafuka Koufukuron

A 5 million yen debt suddenly falls on cash-strapped student, Kamijou Yuuki. Because of his father, Yuuki went through many hardships. After a night out drinking, he comes to on a bed full of ￥10,000 bills with a half naked man?! After waking up, the man even says "I'll give you the money".
Confused, Yuuki escapes and goes home, but he re-encounters the mysterious man, Nao.

"I'll give you the money, so let's have sex. Think of it as physical labor." Nao says, but what does Yuuki do…?