It’s nice to know that Apple is going to provide Japanese users with Reiwa Era support in iOS 12.3. It would have been extra nice if that support could have been in place for the actual start of Reiwa on May 1, but iOS 12.3 should be arriving in a few weeks. If this had been the China market instead of Japan, I’m sure Apple would rushed out a special update beforehand, but I’ll settle for a nice stable iOS 12.3 update. I have not tested macOS Mojave 10.14.5 beta for Reiwa era support, but assume that it’s there as well.
iOS 12.3 is out and recommended for Japanese iPhone users and Apple Pay Suica users, macOS 10.14.5 also supports Reiwa era