I've actually played through Gaiden since making this thread and I'm kind of surprised how much backstory the game did give it. According to a civilian in Mila's temple, the sword was given to Rudolph by Doma and he used it to seal Mila. The cave that you find it in is actually labeled the Rigel treasury. Alm is thee only one allowed in there since he's Rigel royalty (not sure if that's a magical feature or they were just playing by scout honor). Where Doma got it isn't really explained but sinc