Also known as: しあわせなお姫様
From VNDB: "Ritz is an ordinary boy, living a peaceful life. But he is actually a descendant of a royal family! One day, he is surprised to know the fact and he is offered to be next king since the former king passed away a few days ago. He doesn't know what's going on, but he is taken to a palace. He is astonished to hear that he will need to marry in a month...."
