The good news for Japan is that they're getting both the retail and eShop versions of Umihara Kawase Fresh! before the rest of the world does. The bad news is that those who want the retail version will have to wait a bit longer.
Those in Japan who want to snatch the game up through the Switch eShop can hop on the game March 28th, 2019. If the retail choice is more appealing, you'll have to wait until April 25th, 2019. Preloads for the game will go live the same day the Umihara Kawase Fresh! demo is available.