The Japanese pack probably installed some fonts that have higher precedence in WK.
You could set the default font for all pages in the browser, or use a user style with a browser extension (like tampermonkey, but for CSS). That should be a one-liner.
Yeah, of course it was an exaggeration but the screenshot didn’t represent the worst case example. The new font has very thick strokes and little gaps between them making it more difficult to read (and it’s just plain ugly ).
Installing the Japanese Language Pack for Win10 is what did this to you. Your assessment is correct, it was Yu Gothic before and changed to Meiryo. To fix this in Firefox click the three bars in the top right corner of your browser window and go to ‘Options’. There, under ‘General’ you will find ‘Language and Appearance’. Click the ‘Advanced…’ Button. Select Japanese and choose your font. Then uncheck ‘Allow pages to choose their own fonts, instead of your selections above’. Done.
This won’t just affect WaniKani though (so put the check mark back after you’re done with WaniKani for the foreseeable future), but it is the only way I know of to change back to Yu Gothic, since Windows won’t let you uninstall Meiryo.
Also consider searching for the Jitai Font Randomizer here on the forum to, as the name suggests, randomize fonts (during reviews only), so you can get used to the same kanji in different fonts. Imagine only being able to read English in Arial or Times New Roman. But not in Vivaldi, Mistral, Bradley Hand ITC, or friggin Jokerman, or Curlz MT.
I ended up deleting the font altogether. It was a “protected system font” but it’s possible to delete it by taking ownership of the font file, giving the admin user full permissions and then removing it.
I’m pretty sure it wasn’t there before I installed the IME, so I hope nothing breaks
Open the Fonts folder, right click on the font you want to delete, got to Properties, in Security tab (if I’m not mistaken) got to Advanced settings, then find Owner -> change, then you’ll need to type the name of the group you want to change the ownership to. Type “Administrators” and click a button to the right of the text field to find the exact group name. Accept chanes, close the dialogue and go to the font properties, Permissions, now grant All Rights to the Administrator group. Save and closs the dialogue.
Now you can delete the file. Of course it assumes that you’re using a user account with Administrator rights.
You will need to delete two font files: regular and italic.