Sealed Weapon

Sealed Weapons are an item obtained from Treasure Chests that appears in Hyrule Warriors. When obtained from a Treasure Chest, they unlock either new weapon types (ones obtained in either Legends or Free Mode) or higher level weapons (those found in Adventure Mode) on the results screen after completing a scenario. Weapons obtained from Sealed Weapons are zero star weapons with empty skill slots and basic attack power (Attack Power is based on the weapon's level and number of stars) for a weapon of its specific level (from default Level 1 to Level 3). Once a Sealed Weapon obtained from a scenario, a bag containing a random weapon will appear in the chest on subsequent playthroughs of that scenario.

Legends Mode
Sealed Weapons found in Legends and Free Mode (which is basically a Free Play version of Legends Mode that allows one to play with any playable character that has been unlocked) are new weapons that serve as alternative weapon-based movesets that differ from the characters default weapon movesets. These include weapons like Link's Magic Rod, Impa's Naginata, or Lana's Spear. These weapons are usually default Level 1 weapons such as Link's Fire Rod which is his default Level 1 Magic Rod.

Adventure Mode
Sealed Weapons found in Adventure Mode require the player to receive a Gold A rank in specific scenario in order for the Treasure Chests containing them to appear after achieving victory (by completing the main objective of said scenario) in a scenario.