Yo-kai Watch 2 comes out in Japan tomorrow, but the game shipped with a bug that says it doesn’t recognize save data when you first start the game. Level-5 already created a patch to fix the issue, which will be available on the Nintendo eShop the same day Yo-kai Watch 2 launches in Japan.
If you purchase the downloadable version of Yo-kai Watch 2, you will already have the patch installed. You can check to see if the patch is installed by looking at the version of the game. If it is version 1.1, you have the latest version of Yo-kai Watch 2.