>>106448149
I didn't have the specific Mona font you're using, but I found a few TrueType Mona font alternatives online. The one I'm using is:
https://github.com/public-domain/mona
I found it more accurate than the Monapo font that some Linux distros package for this purpose.
(defface shift-jis-art
'((t :font "Mona 12"))
"The face for Shift_JIS artwork, which requires an appropriate font,
e.g. Mona font.")

That nobreak stuff you mentioned in your comments was really important too. I actually didn't notice your comment until after I had searched the web looking for an answer.
(set-face-attribute 'nobreak-space nil :underline nil)