Before Emperor Hirohito died in 1989, the government secretly weighed five dates for Japan to adopt a new era name, official documents have shown, giving a glimpse into the process leading up to the country's transition from Showa to Heisei.

To avoid public confusion, internal discussions at the time revolved around changing the era name of Showa a day after the emperor's death, according to the documents, obtained by Kyodo News on Saturday through a right-to-know request.

The government does not say how and when it decided on the current era name Heisei, meaning "achieving peace," and whose idea it was, fearing that disclosing such information would affect future decision-making.