The decision
Emperor Emeritus Akihito always believed that "the Emperor must be fully capable of carrying out his duties as the symbol of the State stipulated by the constitution while he is on the throne." Once it became difficult for him to fulfill his duties, he believed it was his duty to step down.
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Inner struggle
While the Emperor Emeritus wanted to publicly announce his wish as soon as possible, there were some people close to him who wanted him to change his mind. [...]
Empress Emerita Michiko had a difficult time understanding her husband's wish at first, but later became supportive.
In the year before the video message, the agency quietly approached the Prime Minister's office and began making preparations. One of the original ideas was for the Emperor Emeritus to announce his thoughts on his birthday in December, but that was shelved. [...]
Because the Imperial system is part of the constitution, it is difficult for an Emperor to express opinions on it.
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NHK first reported on the Emperor Emeritus' wish to abdicate when his public address was still being polished. Sources tell me that as reports began to circulate, people expressed their support, and the draft was changed to more definitively reflect his thoughts. In that sense, the understanding and sympathy of the Japanese people emboldened the Emperor to clearly state his thoughts.
When did thoughts of abdication begin?
Taichiro Mitani, former advisor to the Imperial family, says he first learned about the Emperor Emeritus' wish to abdicate back in July 2010 at a meeting at the Imperial Palace. The Emperor Emeritus had already revealed his wish to the Grand Steward of the Imperial Household Agency, as well as Empress Emerita Michiko and their sons, current Emperor Naruhito and Crown Prince Akishino.
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There were two formative experiences behind his decision. One was seeing his father, Emperor Showa, battle illness, almost to the point of unconsciousness in the months prior to his death, while still on the throne. The second was watching his mother, Empress Kojun, weaken in her later years.
Choosing the appropriate time to abdicate
Though his wish was kept private, the Emperor Emeritus seems to have wanted to abdicate in the spring of this year, at around the turn of the fiscal year. When he first told his aides he wanted to step down, he is said to have suggested he was willing to remain on the throne until he was 80. As discussions continued, he is said to have vowed to "keep trying hard until the 30th year of Heisei."
[...] This was in part due to ceremonies planned to mark the 30th anniversary of the death of Emperor Showa in January. The Emperor Emeritus appears to have wanted to carry out these ceremonies himself.
Meanwhile, Empress Emerita Michiko appears to have raised the possibility of her husband abdicating a year earlier, at the turn of the fiscal 2018.
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