What are Sealed Weapons?

Every so often, I come across a chest that contains a 'Sealed Weapon' - the on-screen text tells me I'll have to find out what it is later... and then it never seems to be mentioned again.

I had assumed at first that it was just a weapon, as the game shows you all the collected weapons at the end of the stage. However, I couldn't see any way to distinguish the Sealed Weapon from any of the other random weapons collected in the stage, so I assume I'm on the wrong track.

What are they?

Sealed weapons are what you get when you get a weapon (or a weapon tier upgrade) for the first time. It keeps the suspense of what it is you got until you finish your current quest.

For example, the Fire Rod or Gauntlets for Link, the first time you get them, will be sealed weapons. But you'll get them at the end of the quest, and every Fire Rod or Gauntlet you get from then on is just a regular weapon.

Also, since each weapon also has levels (or tiers, or whatever you want to call it), the first time you get a weapon of that tier (most likely at the end of a quest in Adventure Mode, for A-ranking it) will also be a sealed weapon. For example, the Level 2 Fire Rod is called the Prism Rod. It works exactly the same, it just looks slightly differently, and all Fire Rod attacks don't change. The first time you get one, it will be a sealed weapon.

It's just the game denoting you've gotten a weapon you haven't gotten before.