The Opal Belt is both an item and a title fought for anually by the greatest Erz warriors ever. The belt itself is quite heavy, though it's nothing for an Erz.
The Opal belt is not only beautiful, it gifts it's wearer with amazing strength.
In between annual tournaments, the belt is worn by the winner from the previous year. At the start of the tournament, the winner returns it, and it is kept hidden until the time comes to crown the newest champion.