Somehow I have been using the FM Towns driver for a long time without realizing that the text on the BIOS boot screen didn't make any sense. I took a look at how the video code calculates the font ROM offset and it turned out to be slightly wrong, so it was displaying the wrong kanji. I've sent a PR that fixes it, so now there is real, understandable Japanese text:
Instead of weird gibberish:
It's quite amusing how it only affected kanji, so at a quick glance it *almost* looks like actual text but it's actually pure nonsense.