Without access to a Japanese browser I'm assuming (as others have) that the issue is at the font level. i.e. there is no glyph for the code point U+2630.
Assuming that your page is also served correctly with the encoding as Content-Type: text/html; charset=UTF-8
the issue of HTML encoding should be redundant.
Personally I would use an icon font like Font Awesome to guarantee rendering in all browsers/platforms. Japanese browsers aside, you just don't know what platforms have missing glyphs in their fonts.
As others have pointed out, font files can be large, so I would use the excellent IcoMoon to create a custom font with only the glyphs I need. I do this on my site with 94 icons from various packages and the font files are about 23k.
Alternatively (and for this example, quickest) you could use a standard Unicode font like Google's Noto Sans. Google fonts also allow you to request only the symbols you need, so you can keep the size small there too.
See my example Codepen pulling just one glyph from Noto Sans.