<?php

$s = "\xE6\xA0\xBC\xE6\x8B\x89";
echo "Raw: $s\n";

$j = preg_replace('/^"(.*)"$/', '$1', json_encode($s));
echo "JSON: $j\n";

$e = preg_replace('/\\\\u([0-9a-f]{4})/', '&#$1;', $j);
echo "Entity: $e\n";

echo "Synthesis: " . preg_replace('/\\\\u([0-9a-f]{4})/', '&#$1;',
     preg_replace('/^"(.*)"$/', '$1', json_encode($s)));