I have noticed that when using MySQL, PHP, and PHPmyAdmin, that kanji characters submitted are automatically converted to HTML entities. If course, you could do this explicitly, as well. While these are thus illegible to a reader when you look at the HTML and in the db, they are displayed properly in browsers.
Also, the mbstring library is designed for handling Japanese, and other multi-byte characters. Though it must be explicitly installed with PHP. This page should help.
If you need further assistance, feel free to send me a private message or email.