Thanks to dass for finding this!

The password screen used to be inaccessible on the japanese version, but now it turns out there are inputs you can do at the title screen to access it. This is good news because now a memory card is no longer needed for practicing 100% on console and now things like respawn cycles carried across gem screens and key bonus rounds can be practiced without first having to make a save file. Here are the inputs:

Up Up Down Down Left Right Left Right Left Right Circle