Troubleshoot Japanese on Mac when rectangles display
On your Mac, do any of the following:
If you see a rectangle instead of a symbol: The symbol you want may not be available in the font being used in the candidate window. Click the Input menu in the menu bar, choose Open Japanese - Kana Settings or Open Japanese - Romaji Settings, click Japanese - Kana or Japanese - Romaji in the sidebar, click the Font pop-up menu, then choose a font.
If you’re using Live Conversion: Try turning it off. Converting every character may cause rectangles or wrong characters to display. Instead, use traditional conversion.