Akihito, 83, had cancer surgery in 2003 and then underwent heart bypass surgery in 2012, and he publicly suggested a year ago that his ongoing health problems were interfering with his duties. He has been on the throne since 1989, when he succeeded his father, Shōwa. When Akihito steps down, at the end of 2018, he will be succeeded by his eldest son, Crown Prince Naruhito.

A new law was necessary because the current laws concerning the imperial household, passed in the wake of the American occupation after the end of World War II, do not permit a living succession.

Japan's upper house, the House of Councillors, passed the law, which is designed to be a one-off, applying only to Akihito. The law also includes a nonbinding resolution that tasks the government with finding a way to ensure a smooth succession going forward, even if the next person in line to the throne is a woman.

The last emperor to abdicate the Chrysanthemum throne, Kokaku, stepped aside in 1817 and was succeeded by his son Ninkō.