Prime Minister Shinzo Abe's Cabinet approved legislation Friday allowing Japan's emperor to abdicate the throne. If the bill passes parliament and if Emperor Akihito steps down, the event will mark Japan's first abdication in 200 years.

Akihito heads the oldest hereditary monarchy in the world. In a rare televised address last year, the 83-year-old expressed a desire to retire and give his son time to rule: "When I consider that my fitness level is gradually declining, I am worried that it may become difficult for me to carry out my duties as the symbol of the state with my whole being as I have done until now.'

The bill is a one-time provision for the emperor step down while he is still alive. Next in line for succession is Crown Prince Naruhito, who is 57.

As The New York Times explains, "Any decision regarding the emperor is freighted in Japan, where until World War II, he was seen as a god. The postwar Constitution, written by American occupiers, stripped the emperor of his status as a deity and set him up instead as a symbol of Japanese unity."

Imperial law is strict: Succession to the Chrysanthemum Throne must be posthumous and only males are eligible, as Kyodo News reports.

The Japanese public overwhelmingly supports allowing emperors to retire, according to Kyodo, but conservative supporters of Abe's Liberal Democratic Party want to avoid making permanent changes to the laws that govern succession.

One factor in their aversion is a fear is that changes in the Imperial Household Law would lead to women becoming rightful heirs to the throne. The bill in its current form does no such thing, but the opposition Democratic Party has been advocating for debate on allowing princesses to remain in the royal family after they marry commoners.

That issue is especially timely: News broke this week that the emperor's eldest granddaughter, Princess Mako, will soon be engaged. If and when she marries, she will no longer be royalty.

There are few male descendants eligible to succeed. As the Times notes, "Under current law, Naruhito's successor would be his younger brother, Prince Akishino, 51. Akishino's son, Prince Hisahito, 10, is the only boy of his generation in the imperial family.

If Akihito abdicates, it may happen when he turns 85 in December 2018, according to Kyodo News. A series of rituals will take place over the course of a year, based on ceremonial practices from Japan's history.

Abdication used to be a common practice; according to Kyodo, about half of Japan's 124 former emperors did so. But a law created in 1889 (and a 1947 update to it) made abdication impossible, as it sought to eliminate threats of still-powerful former emperors.

The last emperor to abdicated did so in 1817, The Asahi Shimbun reports.

"It is urgent that the system should be reformed so that female members can remain in the imperial family," Isao Tokoro, professor emeritus of legal history at Kyoto Sangyo University, told the Times. "Otherwise, we will lose more and more members from the imperial family."

Tokoro noted that before the current law was put in place in 1947, Japan had eight female emperors — who "did wonderful jobs."

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