The yellow dragon guards the Yooguk kingdom in a realm where there are five kingdoms. On the other hand, Doijin is a hard working mortal from the human realm who while walking home from work, got hit by a truck and wakes up in this different realm where he is the so called emperor who has to follow what the golden dragon says, if he wants to go back home to his sister and niece.
Shu used to be a 31 year old man in Japan but he died while trying to save a older woman. He only remembers the truck speeding towards him but then he woke up in a carrige in a different world. However, he was on his way to be sold off as rich mens sex slave.
Futaribocchi no Ever After