In the era of the Hero of Time, in Termina, currently under the rule of Majora – which, due to conflicting histories and many eyewitness testimonies of time running amok, may or may not have lasted for three days. Location – Inside the Moon. Somehow:
It was a fact that nobody but the two of them really knew, for a multitude of reasons. One of them was that it had been so very long ago that nobody besides the two of them remembered. But a second reason could have been that both of them were currently masks, and nobody thought of masks as being able to have genealogy anyway.
In any case, the Fierce Deity was Majora's half-brother, and neither of them were happy about it.
The Fierce Deity hadn't been too big on it because Majora was an insane wackjob. Majora, on the other hand, had been unhappy about it for rather more complicated reasons.
Majora wanted nothing less than to rule the world. The Deity, for his part, through battle prowess and a ridiculous amount of coincidental luck, had managed to get himself anointed King. Majora had taken one look at this and said, 'Nope, not letting that slide,' and had thus staged a coup and had the Deity thrown in a dungeon cell that he then promptly forgot about. Eventually, because Majora had also forgotten to post guards, the Fierce Deity broke himself free and started a war on his half-brother that ended in the both of them being sealed in masks because the citizens finally got fed up with the two of them fighting and hired a passerby sorcerer to deal with it.
Unfortunately for the Deity, Majora had been sealed first, and thus took advantage of his half-brother's disorientation by trapping him in a forgotten corner of his own mindscape, where despite what past experience should have told him, he immediately forgot all about it.
And naturally, this once again came back to bite him later.
Under the massive tree that was somehow inside the Moon, the small boy wearing the mask of Majora shyly handed the Hero of Time a pale white mask with red-and-blue tattoos.
"I found this on the ground in a dark place," the boy said. "I think you should have it. His name is the Fierce Deity. I hope you can control it..."
Ten minutes later, the Hero of Time used the Fierce Deity to smack Majora silly.
Link slowly looked up from the very, very, very old lineage book he'd dug out of the Royal Public Library after noticing an interesting coincidence in the histories of Termina he'd come across while following the Hero of Time's adventures.
"...Alright, I did not see that coming," he admitted. "Good to know, though... putting that one on the list."
Rule Number Three: My noble half-brother whose throne I usurped will be killed, not kept anonymously imprisoned in a forgotten cell of my dungeon.
