Hurrah! I have success! Limited success, anyway.
I found that if I set up Windows shortcuts to change the input language from EN to JP (and back), then when I found I couldn’t type or access the menu within the game, I could swap language and it’d work. For a bit, and then I’d have to swap again. But it works!
Then I realised that my joypad (a GC pad through a USB adapter) doesn’t let me go “full speed”. That is to say, I push forward fully, and my character walks instead of runs. Needless to say, that caused tedium beyond tedium. Finally making it onto the planet’s surface, I ran into the Rappy Festival. Sadly, you can’t kill the stupid yellow birds, but the Samba de Amigo music playing in the background was nice, if a little unexpected. Blew up some crates instead, before getting really annoyed at my lack of running sk1llZ and gave up.