To be filed under ‘you learn something new every day’ — a series of potential millennium bug-style issues that could be faced when Emperor Akihito of Japan abdicates. Japanese calendars effectively begin from zero with a new era every time there is a new emperor.
Akihito has been on the throne for almost the entirety of the information age, meaning that many systems have never had to deal with a switchover in era.
Moreover, Unicode will have to create a new character to represent the new era — which has not yet been named. This clashes awkwardly with the planned release of Unicode 12.0.
But this is the most incredible scenario:
Many older computers, with aspects dating back to before the end of the Shōwa era in 1989, have never been updated to reflect the new era, and still think the year is Shōwa 93. That means Japan could face another mini Y2K problem in 2025, as those systems attempt to tick over to a three digit Shōwa year they can’t cope with.