Senji Muramasa was a blacksmith widely known for his powerful blades. Unfortunately, these blades were cursed with their master's madness, enticing a great bloodlust in those who held them. He is also technically one of the protagonists, making 5.
It is said that a Muramasa can cut through anything. However, it cannot be sheathed until it has drawn blood, be it the enemie's or it's wielder's. Only those who utilize the Oboro style can wield these powerful blades without becoming thralls to their will.
Muramasa was condemned to craft blades eternally as punishment for the creation of these foul blades.
During the game, the player can have him forge powerful Demon Blades by utilizing the souls of enemies, as well as the player's spirit (collected by eating food).