Keys for the King of Swords

Keys composed of a mysterious black metal. The King of Swords will take them in trade for training you.
100 Keys and you can train to learn a sword technique. 100 Keys and you can train to learn features from other styles of your class.
10 Keys can be melded into a Greater Key 100 Keys can be melded into a key that unlocks a door to a demon lord, as well as his hoard loot.