Funnily enough, Akihito will be following earlier traditions in abdicating. Japanese Emperors did not always reign their entire lives. The 1817 abdication of Emperor Kōkaku was actually a moment of transition between two eras: Before Kōkaku's reign, Emperors (if they didn't die young) abdicated after a relatively short reign. Kōkaku was the first Emperor in about 250 years to stay on the throne past his fortieth birthday. He ruled from 1799-1817 and during his reign, was extremely involved in reviving some of the prestige and authority of the Imperial court. Kōkaku did finally abdicate, only dying in 1840, but no Emperor since him has abdicated.

The reasons for the constant abdications of Emperors in Japanese history are multiple. As you may know, through much of Japanese history, the Emperor has been closer to a ceremonial figurehead than a direct ruler. In the Heian court, a thousand years ago, the powerful Fujiwara family controlled the Emperor and it suited them for the Emperor to marry a Fujiwara bride, sire a son, and then quickly abdicate in favour of the child. (Repeat as many times as possible.) Later on in the Heian period, Emperors with real ambitions to power realized that they could more easily exert that power as retired Emperors, the power behind their successor's thrones.

But in the Edo Period, the period in which Kōkaku abdicated, the regular abdication of Emperors was part of the Shogunate's policy to keep the office of Emperor as ritually important, but without allowing any one Emperor to build up power. Kōkaku's long reign, and the lack of abdications following him coincide with a period of growing national respect for the Emperor's role. Fifty years after Kōkaku abdicated, the Emperor was officially restored to the head of the new modern Japanese state.