...And so the Princess of Twilight retreated once more from the world of Light; with her she took the hope of her return, and behind her she left the Hero that cleaved Light and Shadow for her sake.
☪ a hero without purpose
Seven years ago, King Ganondorf of the Gerudo, bearer of the Triforce of Power, died. Seven years ago, Princess Midna of the Twili, to seal the road between the realms forever, shattered the Mirror of Twilight. Seven years ago, Sir Link of Ordon, Hero of Light, wielder of the Blade of Evil's Bane and bearer of the Triforce of Courage, attempted to pick up the shards of his old life.
And seven years ago, for the first time since he donned the proud green clothes of the Goddesses' holy warrior, Link failed. The boy from Ordon, the carefree ranch-hand who loved Ilia and protected Colin, was gone forever; left in his place was a tired, jaded, heartbroken hero with no quest left to complete and no happy ending to go home to.
Clearly, a new quest was in order. This time not for Hyrule, not to rescue a princess or save a realm. No, this was not a quest Link undertook as a hero or for any great cause, but instead a quest for himself, as a man in search of the woman he loved.
Three years ago in Castletown, Link met a man who smiled and laughed and lamented his terrible fate. This man told him of a holy artifact, a sacred, blasphemous mask with the power to grant whatever the wearer wanted--so long as they were strong enough to control it. The quest for Midna became a quest for a mask, for the last remaining path to her side.
One year ago, buried in a holy forest and guarded by a monster child and his wooden puppets, Link found the mask of the Demon God.
Quite recently, after a year of concentration on harnessing the destruction the mask could cause, Link finally found in himself the power to control it, to harness the strength of a god enough to take him very far from home.
More recently still, Link found his ability to realmshift is impeccable--it's his aim that seems to be lacking.
☪ a god without restraint
Here is where the Hero of Light finds himself in trouble. Link, being who and what he is, is more capable of standing against the will of the god in the mask than anyone else in the world, as well as more comfortable with the transformation. He was a monster once, he can do it again--rearranging bone and sinew and keeping his mind intact is nothing new.
The problem lies in Link's new ability to shift between realms. The ebb and flow of magic in Hyrule, his Hyrule, is familiar; he can move with it, trace the leylines in his mind's eye and only tap into the power he absolutely needs, to do those things he absolutely needs to do.
Away from home, things are different. The magic itself is different, and his eyes are blind to its veinwork. The mask, his conduit to tapping into this power, activates in ways that Link can't control--ways he can't reverse so long as he's away from his home.
The Demon God, all ash-whiteness and blood, fuses with the Hero of Light. The mask ceases to be just a mask, the seam in his flesh goes smooth, and the Triforce shining in him is the only thing keeping the monster he's merged with from swallowing him whole. As it did in the Twilight, the Triforce keeps Link's mind his own, intact and unharmed by the change; but only for now.
In the end, gods always overpower their children. Even after a year of practice, Link can still just barely feel the subtle manipulations inside him; negative emotions made more intense, simple annoyances suddenly beyond his ability to ignore.
It's just a matter of time.