How to typeset Japanese with advanced features in (Xe)LaTeX.

japanese-full.tex

\documentclass[12pt]{article}

\usepackage{xltxtra, setspace}

%% fonts

% xeCJK options from <http://mesokosmos.blogger.de/stories/1818274/>:
\usepackage[%
  boldfont,
  CJKnumber,
  CJKchecksingle
]{xeCJK}

% main font for CJK input from <http://www.fontpark.net/en/font/kozuka-gothic-pro-m/>
\setCJKmainfont[Script=CJK]{Kozuka Gothic Pro M}
% \setCJKmainfont[Script=CJK]{Kozuka Mincho Pro}

% version of the above font with rotated characters for vertical text,
%  font needs to come with ``vrt2'' feature
\setCJKfamilyfont{cjk-vert}[Script=CJK,RawFeature=vertical]{Kozuka Gothic Pro M}
% \setCJKfamilyfont{cjk-vert}[Script=CJK,RawFeature=vertical]{Kozuka Mincho Pro}

% main font for non-CJK input from <http://www.exljbris.com/delicious.html>
\setmainfont[Mapping=tex-text, SmallCapsFont={Delicious SmallCaps}]{Delicious-Roman}

%% Furigana

% use \ruby{kanji}{kana} to set Furigana
\usepackage[CJK,overlap]{ruby}
% position of Furigana: below/right
\renewcommand{\rubysep}{-3.9ex}
% increase line space for Furigana
\onehalfspacing

%% alignment

% also from <http://mesokosmos.blogger.de/stories/1818274/>:
\XeTeXlinebreaklocale "ja"
\XeTeXlinebreakskip=0em plus 0.1em minus 0.01em
% we also drop paragraph indentation in order to get proper alignment
\setlength{\parindent}{0pt}

\begin{document}

\section*{Regular English Text}

This is \textbf{English} text and should be \textit{set} in Delicious
(or \textsc{Delicious SmallCaps}).

\section*{Regular Japanese Text}

きのう、ラースは　\ruby{山}{やま}\ruby{本}{もと}を　あいました。　
「こんにちは、\ruby{山}{やま}\ruby{本}{もと}さん。おげんき　ですか。」

% こんにちは、わたしは　ドイツ\ruby{人}{じん}　です。\\
% これは「にほんご」です。

Note the nice alignment of the letters, in spite of the 「」 brackets.
(Some combinations of punctuation might break the alignment, though.)

\section*{Vertical Japanese Text}

\begin{figure}[h!]
\begin{center}
\rotatebox{-90}{
\begin{minipage}{0.35\textwidth}
\CJKfamily{cjk-vert}
\onehalfspacing % needs to be repeated here (?!)
きのう、\textbf{ラース}は　\ruby{山}{やま}\ruby{本}{もと}を　あいました。 
「こんにちは、\ruby{山}{やま}\ruby{本}{もと}さん。おげんき　ですか。」
\end{minipage}
}
\end{center}
\end{figure}

That's quite a nice alignment of the letters, in spite of the 「」 brackets
and the (artificially created) bold letters. (Some combinations of punctuation
might break the alignment, though.)

\end{document}

japanese-minimal.tex

\documentclass{article}

\usepackage{xltxtra}

\setmainfont[Mapping=tex-text]{Kozuka Gothic Pro M}

\begin{document}

hello = こんにちは

\end{document}