You will need a Japanese font.
basic rendering
Compare to the reference graphic below the test.
Assertion: When simple ruby markup is used, the ruby text appears above the base text at approximately half the font size.
Notes:
The Ruby Annotation spec recommends non-normatively that, in the absence of other style information, simple ruby markup should place the ruby text before (ie. above in this case) the base text. This is also the initial value for the CSS3 Ruby Module draft.