while i was developing a Japanese website for my client, i encountered the following:

in the screenshot, the hiragana/katakana rendering and the kanji rendering look like it’s using two different fonts
in google chrome and other modern browsers:

it’s not limited to japanese only, if I use Simplified Chinese(GB2312), this kind of issue happens as well; Traditional Chinese(Big5) have no such issue
the rendering in IE looks terrible, the major audiences will be using IE, how can i solve this issue?
I did not specify any font in CSS
Most probably, the rendering does use two (or more) different fonts. To fix this, specify a list of fonts for the content, selecting the fonts so that a) each of them contains all the characters you are using and b) the computers that your visitors will use contain at least one of those fonts.
As a rough starting point, check out http://en.wikipedia.org/wiki/List_of_Microsoft_Windows_fonts
The reason for different browser behavior is that browsers have different default fonts and fallback strategies (for selecting alternate fonts when the browser’s default font does not contain all the characters needed).
It’s also a good idea to declare the language:
<html lang="ja">. It may affect font choice by a browser, so that a font suitable for Japanese is selected. But this normally does not matter when you specify fonts in your document.