Weapon Ascension Material.
An intricate device once called "the Seven Gadgets of the Legendary Thief". It is rumored to be invented by the legendary thief Reed Miller whose name is known far and wide.
Just as the original Treasure Hoarder was an assembly of all kinds of people, by combining multiple gadgets that were meant for different purposes, one could break through artificial boundaries, whether they were chains or borders.
The number of tools contained therein is not limited to seven categories, only that people are accustomed to using seven to describe anything that is numerous. Perhaps it is for the same reason that the world is believed to have only seven orders.