The manga included a big beast that looks like the thing the Avatar rides around on that Nickelodeon show....But meaner. It wore armor that would grant wishes to whoever wore it, so people would often come to challenge it to a fight to try and kill it and take its armor. Well one day someone came along. The adventurer looked a lot like the Fierce Diety. The beast would eat its challengers and was never happy because it never had a real challenge, or a friend, or whatever, so the adventurer played a tune on his drum for days until the beast danced itself to death.
That is a very basic, relying on memory, recap of the manga by the way.
Now, since the manga is not canon, it can be at least believable that the posibility is there for it to be true according to some things in the game itself. Majora's Incarnation (the second version of the Majora's Mask final battle) dances around. You got a mask that resembles the guy who actually killed the beast in the manga, now fighting the mask supposidly carved from its armor.