Mine

using System;

public class Test {

	public static void Main (string [] args)
	{
		string str;
		int i;
		char ret;

		str = "a%E3%81%8B";
		i = 1;
		ret = Uri.HexUnescape (str, ref i);
		Console.WriteLine ("ret={0} i={1}", (int) ret, i);

		str = "a%F0%90%84%80b";
		i = 1;
		ret = Uri.HexUnescape (str, ref i);
		Console.WriteLine ("ret={0} i={1}", (int) ret, i);
		
	}

}