Japanese text with furigana

[Caagr98]

I'm trying to insert a bit of Japanese text in some markup. Putting the text 
itself works fine, but as soon as I try adding furigana (small kana above the 
kanji), it looks terrible. Is there anything I can do about that?

——————

\version "2.19.80"

#(define-markup-command (furi layout props kanji kana) (markup? markup?)
   (interpret-markup layout props
     (markup
      (#:override '(baseline-skip . 0)
        #:center-column
         (#:magnify 1/2 kana
          kanji)))))

\markup {
  \box 一番 % Works fine
}

\markup {
  \box \concat { % Terribly misaligned
    \furi 一 "いち"
    \furi 番 "ばん"
  }
}

furigana.png
Description: PNG image