I think it's too late to suggest this, since you appear to have completely filled the printable characters with the kana glyphs, but just in case there's something to spare somewhere:

I just used one of the unicode thumb glyphs (👎,👍) and realized it'd be handy to have such glyphs in the PICO-8 character set.

I drew up some possible 7x5 PICO-8 glyphs for them:

You could type them with -/+ in glyph mode.

Even if they can't be fit into PICO-8 itself, the thumb-up might be good for the BBS, because I think a lot of people don't realize that's what the ★ glyph on BBS posts is for, given how seldom it seems to be used.

(I guess it's not a big deal if this isn't possible, though, since we can obviously just draw them manually.)