These are known through the game as Divine Instruments. They can be optained through defeating bosses and buying them from merchants. Some even grant elemental powers whenever Amaterasu needs it. Two Divine Instruments can be equipped at a time, one as a main weapon and another as a sub. Each weapon acts differently depending on what it's set to.
When you start a new game all weapons will be brought pasulong to the new file except the final tier weapons.

The Reflector
The ancient mirror treasure was used, not as a mirror in the modern sense, but as a ceremonial object. We tried out a lot of...