Kafuka KoufukuronYes No Happiness ; Theory of a Possible Happiness ; 可不可幸福論

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?