Furiganify!

Furiganify! is a lightweight extension for Safari that adds Furigana reading aids (Ruby characters) to Japanese text.  All processing occurs on your device to ensure maximum privacy. Furiganify only reads the content from webpages you explicitly select. No data about the webpages you visit or their content ever leaves your device. Both Latin characters (Romaji) and Hiragana can be used. In addition, you can also chose to have furigana added only to Kanji characters beyond a certain school grade or JLPT level. This reduces clutter and serves as a great studying aid.