character taking 6 bytes

It probably holds HTML entities in a string. Like 燃 or possibly the URL style, %8C%9A. Or maybe UTF7, like [Ay76b. (I made up those values, but your actual ones will be similar). It is always a pain to rely on any framework with character encoding because its authors were likely U.S. or European, both sufficing with simple ANSI where one byte equals one character.If you managed to understand your encoding and converted it to the real UTF8 or even UTF16, it would take up less space in this particular case.

You probably literally have:

\u682a\u5f0f\u4f1a\u793e\u30a8\u30b9\u30fb\u30c0\u30d6\u30ea\u30e5\u30fc\u30fb\u30b3\u30df\u30e5\u30cb\u30b1\u30fc\u30b7\u30e7\u30f3\u30ba

See:

"\u682a\u5f0f\u4f1a\u793e\u30a8\u30b9\u30fb\u30c0\u30d6\u30ea\u30e5\u30fc\u30fb\u30b3\u30df\u30e5\u30cb\u30b1\u30fc\u30b7\u30e7\u30f3\u30ba".length();//23, or 69 UTF-8 bytes

Vs:

"\\u682a\\u5f0f\\u4f1a\\u793e\\u30a8\\u30b9\\u30fb\\u30c0\\u30d6\\u30ea\\u30e5\\u30fc\\u30fb\\u30b3\\u30df\\u30e5\\u30cb\\u30b1\\u30fc\\u30b7\\u30e7\\u30f3\\u30ba".length();//138, or 138 UTF-8 bytes