The Constants were an old tale, so old that they were acknowledged as more myth than fact even when Thranduil stood no higher than Oropher's knees. The elves were the only ones who had a yarn spun of that particular thread, rightly so, as they were the only ones long-lived enough to have a chance at seeing one. It was so said when Thranduil asked the high elves of an encounter he'd had in the woods. A creature yet unnamed, the thing stood glittering with dew on the forest moss, a regal beauty that was lost with the old world. Its eyes glittered an impossible swirl at him, and it breathed with silk-spun tones in to the wind "Many tales are yet untold, dear starlight." and endless the words echoed through time, a promise thrumming with a magic Thranduil had no knowledge of. And he knew then that this, this being, this soul, was Constant.
The thing disappeared while his young, receptive bones vibrated with the magic and Thranduil ran home, his heart pounding and his head swimming and very little true thought was put into the encounter until much later.
A Constant, a being of innumerable lives, a thing that remained though its shell changed. It was a stubborn soul that never moved on, only returned again and again in the life of a particular elf as if somehow tied to them. It was, as he quickly learned, something the high elves had long since cast doubt on as coincidence. A thousand years gave plenty opportunity for any set of circumstances to repeat themselves, after all.
He told Oropher of it, the woodland creature of such beauty and significance, and at last found an open ear. But Oropher seemed only to be indulgent rather than believing and Thranduil's young pride wanted none of it. So he kept it to himself, and not long after his encounter the woods inhabited by those strange and beautiful creatures burned tragically to ash.
But the soul did not leave middle earth.
The words were the Marker, it seemed, and as time wore on his Constant became easier and easier to spot for it. "Many tales are yet untold, dear starlight," it would say, in the same tongue it had first spoken the words. An increasingly ancient and out of place language, one that died out before many races were counting time.
They met again as Elf and Númenórean, and again the creature spoke to him "many tales are yet untold, dear starlight." He grinned a noble grin while he carved ships on the piers. He was lost when Numenor sank beneath the sea.
Once, before the feuding started, it was a Dwarf who greeted him so. He was a being flavored with the swifter lives of dwarves, living fast and hard with his whole self, and in his youth Thranduil had taken to watching him. Again the soul was lost to time, and Thranduil wondered at the true intention of such an inconsistent and fleeting being bequeathed upon elves.
It was a Took, once. A very long time before Thranduil considered most of the world settled, the Halflings wandered bravely through his father's forest, bright little things, and one looked at him and said "Many tales are yet untold, dear starlight," and Thranduil had again found the one thing that remained. Hobbits were the shortest lived by far, aside from men, and there was little to be done for it.
There were dozens, and he found himself taking a strange comfort in their presence, and the soul attached to his became something precious. And then, one day, a Vanyar elf maiden traveled to Greenwood, and there she danced with the elves in the forces with a blade of glorious white. And when they met he asked of her history, and she smiled and said "Many tales are yet untold, dear starlight."
It was unheard of. He could scarcely believe it himself, that a constant should manifest as an Elf. A Constant was so named because it was not inherently something that ought to be constant, and had to be called so to be understood. Not like elves. Yet she spoke words so familiar to him in a language long dead, and though cynicism had grown in him over the long years, he could not deny what he faced. He felt, immeasurably, excitement. And oh, the elders still would not believe him, but he paid them no mind - though one looked upon him in warning and said 'they are not meant to be truly constant, my prince. I would fear for the future of a deviation such as this'
They were married in spring. There was nothing so blissful in Thranduil's long and varied history. Her strength and beauty cleansed his heart, her loyalty and kindness soothed his soul. He did not know, but he told her of his secret, delirious with medicine that could never fully heal him after a battle with the ice drakes. 'My heart, my stars, my constant' he spun sonnets, and she looked at him so oddly 'always by my side, now forever as you are'.
A child was born in summer, fair as either of them, and Thranduil was buoyant with delight. Greenwood lit up with celebration, loud and bright and with song and fire for a time no one counted. Elves and men and dwarves came to wish them well and join in the festivities. Eventually it died away, and the impossibilities of his fortune were so far from his mind by then that they seemed a mere dream. He spent his days on clouds, walking with his love and son through starlight and great forests come to life.
And then Sauron came.
He terrorized middle earth, a great calamity of darkness casting the shadows of death upon all. So many skirmishes they fought with their enemy before he fell. So much he stole from them with his final breaths.
Thranduil walked the battlefield, exhausted and grieved by the loss of his father, dogged by the dread of another. He found her lying on cold stone beneath the tower. Panicked he stumbled to her side, lifting her into his arms and holding on as if to keep her longer with his grip alone.
She smiled with her last, and said quietly, "fear not, dear starlight, for we shall meet again." Thranduil did not remember telling her, but he knew he had, and he shook his head. She could not die; she could not leave him to eternity without her. But her eyes went dark before he could say anything.
He locked the gates when he returned home. He forbade any from coming through his kingdom, and he refused to go to theirs unless on a matter that concerned his people. He did not want to meet his constant again. He did not want to face a shadow of her, an outline filled in with a new life. He wanted the mother of his child, and refused to be subject to fate's cruel mimicry of her.
Darkness fell. Evil rose anew. He did not hear the words again for nearly a millennia. At length he grew tired and bold, and when Smaug was defeated he took to his steed and left his land, Mirkwood as it was now called, for the first time in a century, intending to claim what was rightfully his. The humans were no doubt in dire straits, and he spared them a thought before going. The one that remained had been of men, once. They marched on into Dale with purpose, and Thranduil met with their new king, and they readied for war.
In the dark of the tent in which Thranduil did his planning, he decided he quite liked Bard the Dragon Slayer. Bard was a bit bitter himself, bold with it, and held a sense of duty and heroism that was becoming rare in the race of men. Fast comradary was not common in elves, but so it must be with the short-lived humans. Late on the eve before the battle, they spoke plainly together, Bard a bit lose-tongued with wine.
'King and dragon slayer, all at once' Thranduil said in a toast 'you'll no doubt be a legend among your people'
And Bard laughed a humorless laugh, his eyes drifting to the direction where the Lonely Mountain lay, and said in the old tongue 'Many tales are yet untold, dear starlight.'
Thranduil's glass slipped from his fingers. Bard looked back when it shattered on the ground with a sad little sound. 'Where did you learn those words?' he asked.
The bowman looked at him, and his gaze was as old and deep as time. And then it was gone in a blink that left only a bowman again.
Thranduil started to laugh. 'I leave my land for one day' he said, walking near 'and here so quickly you manage to find me.'
Bard looked at him, glassy-eyed but alert, and Thranduil laid their foreheads together and closed his eyes. He had not wanted to look upon another incarnation, but now that he had he was weak to it. Had always been so, in truth. 'How many more times, I wonder' he murmured 'how many must I love you and lose you'
Whatever he thought of Thranduil's words, Bard said nothing. Only finally calloused hands cupped his face, and Thranduil found himself being kissed.
At length the bowman pulled back, a flush on his cheeks not entirely from the wine, and Thranduil looked down at him, helplessly lost long ago to his power.
'I- I am sorry, I don't know what I was-' he stumbled over his words and Thranduil closed the small gap between them once more for a brief moment. Then he stepped back and waived at the door 'You should rest, Dragon Slayer,' he said, turning away to sit 'for tomorrow we may yet go to war.'
Thranduil sat in silence for a long time after Bard said his goodbyes. He thought of the long-lived men of Numenor, of silly, adventurous hobbits, of dwarves as he'd seen them long, long ago, of a creature unnamed in the woods, and of an elven princess. He thought of men, too, their tenacity in the face of a land that offered death at every turn. He thought on all these and more, and of his father and of elves slain in numerous battles throughout history.
He thought, and he did not come to an answer until days later, as the dawn found them counting their dead and, if only in quiet murmurs, planning for their futures. In the cool light of morning he reached a verdict to a question he'd first asked himself long ago. The grand intention of the Constant did not matter. As he watched Bard tend the needs of his people, Thranduil decided his heart was glad for it.