Thank you! That's very good feedback. I've filed an issue at https://github.com/birchill/10ten-ja-reader/issues/1799 and will see what other users think of the change.

At very least, we can restore the hat on the "a" very easily and we could add an option to use a system font too.

Update: We've just released a new version (1.19.1) which adds a setting to use system fonts. Thanks for the feedback!