This is basically URL decoding to the decimal code but nothing in PHPworks how you'd expect it.
Here are online tools to verify and check your work, it's important when querying databases with non-English characters:
http://yehg.net/encoding/index.php#
http://meyerweb.com/eric/tools/dencoder/
http://www.codetable.net/decimal/65398
Japanese:
http://symbolcodes.tlt.psu.edu/bylanguage/japanesechartkatakana.html
Charat code for PHP:........