The Columbus, Ga.-based insurance­ company Aflac Inc., which does a significant portion of its business in Japan, said earnings rose 9 percent in the fourth quarter as premium income rose in Japan, offsetting the impact of a weaker yen. Aflac said net income rose to $581 million, or $1.24 a share, compared to a net of $538 million, or $1.15, a year earlier. Revenue climbed 6.6 percent to $6.38 billion. Analysts, however, expected $1.47 on revenue of $6.42 billion.