Okay so this is entirely au in which Lexa is a goddess and Clarke a mortal just because I needed to write it.
There are times, when the earth is sleeping below you, that you actually feel alone. Most of the time you can feel the hum and whir of the voices and minds that live beneath your feet. It's a strange feeling, being so far away yet feeling so connected, it makes you feel lonely a lot of the time. It's ridiculous, you're a deity, an immortal, a divine being, you shouldn't allow such weaknesses to take root in you. The truth is though the seeds of loneliness began to take root many a millennia ago, and by the time you realised they were there they were too strong to root out.
When the world sleeps, it makes you feel more at ease, sometimes it is almost peaceful. The majority of humanity sleep easy in their beds, their dreams are peaceful and their resting minds tranquil. There are the odd ones whom spend their nights wracked by terrors and their days trying to forget them, but these days they are not as plentiful as they once were.
A pass time of yours, when you are not protecting humanity from one another and upholding the fragile peace that has been formed among them, is watching them sleep. As a divine being you were not gifted with the sweet release of being able to slip away from the world for hours at a time, it makes you wistful at times. When you were placed at your post by your father oh so long ago, you became the watcher of humanity, their sacred protector. With that unimaginable power came huge amounts of responsibility, and so you must watch their every move constantly.
You watch humans sleep in your more quiet moments, their faces mesmerise you, there is something quite beautiful about the way dreams flicker across their faces. Humans are beautiful to watch, but something about them makes you very sad as well, you try never to watch the same human twice. It has become a rule of yours, over the never ending centuries, because their fragile faces age with each watch and in what seems like the blink of an eye to you, you watch them wither and fade with age as their skin sags on their bones.
Many centuries ago, you made the mistake of watching a girl. The first time you saw her, she was very young, barely becoming a woman. There was something captivating about her, although you tried to keep yourself away from seeing her you couldn't, not only because you were all seeing but because it was a need. It came from deep inside of you. You went back to watch her night after night. Until one night you heard her whisper something in her sleep that made you leave for a while. In her sleep she had whispered a name, a name she should never say. A name that made your stomach turn over and your heart feel pain. The name she uttered in her sleep was forbidden, it was your name, Lexa.
Uttering the name of the goddess was forbidden to all, they were supposed to address you as Heda, not that they knew you personally of course. If the girl had been heard she would have been tied to the hooves of a horse and dragged through the streets, if she wasn't dead by the end of it she would have been tortured for committing such a sin. So you had stayed away, hoping that it had simply been her sensing your presence around her whilst she slept.
You didn't stay away for long enough, curiosity got to you, so you found her and found out her name. Costia. It was a pretty name for a pretty, foolish girl. You had materialised in her room and she had woken up before you had left, of course she had. After that you saw her on occasion, in your quieter times. Something about her fascinated you, she intrigued you in ways no human had before.
Stupidly, idiotically, you found yourself falling for a mortal. It became harder for you to stay away. You left her small gifts if she was sleeping when you came, if not you talked. One day, you found yourself arriving slightly earlier than you normally would, you found her doubled over, and she was coughing up blood. Her mortal frame was failing her, and there was nothing you could do to stop it. You watched the mortal girl you had grown to love wither away, you held her and she died in your arms. Although you were the most powerful being on earth you had no jurisdiction over life and death. Even your almighty power could not control that, her life had ended before she was even considered an adult by human standards. The time you had had with her was selfishly cradled by you, you kept it to yourself, not wanting to share it with any one, not that you had any one to share it with. You were alone, which was how it was supposed to be.
Yet, as time passed, as you protected humanity from the threats that it faced, like total and utter destruction, you went back to watching a different human nightly. Secretly, as the decades slipped by barely noticed, you hoped that you would come across Costia's soul reincarnated into a new body. That was what the people of earth believed in, you and a full circle.
It took centuries before you gave up the search, but eventually you gave in to the loneliness you were destined to feel, nursing a broken heart and spirit as your endless watch continued. You continued with the job you specifically had been chosen for, you let it consume you if only to be distracted from the endless pain you felt.
The delicate and tentative peace between people became strained again, you heard whispers of nuclear war and radiation. Whispers of all consuming fire and death reached you, as you guarded your people from above. The whispers became more urgent as time went on, people grew wary as they began to feel as though their prayers were going unanswered. You began to set things right again, you strengthened the peace across the vast world beneath you, and for a time all grew quiet once again.
With the quiet came time, far too much in your opinion. You took up a new pass time, you began to materialise throughout the world and wander the streets for an hour here or there. During one of your wanders you spot a girl. You're in Paris wandering absently along the Seine when you see her for the first time. Her eyes are green and her hair is the same golden blonde as Costia's had been- but you can't think like that, not when you know that loving a mortal makes you weak. You have a world to protect so you can't think about yourself or the possibly reincarnated soul of your lost love.
Through the centuries that have passed since you lost her you have grown, you have matured in a way you're not sure you like. Now you know better (or at least that's what you tell yourself) but you know that you must know better. After all love is weakness and weakness equates to selfishness when you have a world to protect, any weakness you have should be compartmentalised and broken down so that it is manageable. If it becomes manageable then it can be controlled, if it can be controlled then it is no longer a weakness.
Still as you hurry past you find yourself looking back at the girl, her eyes meet yours and she smiles softly, as though she knows something you do not which is of course ridiculous. She is sketching something,but she pauses as you walk past. You get a glimpse of the drawing as you walk past and somehow you end up staring slack jawed at the picture. It is a picture of you, how you really look, not how oh are perceived. The picture is titled with the word Heda but you're almost certain your real name is hidden in there some where.
You finally manage to gather your composure, at least, enough to stop gaping at the street artist who just knows what you look like, you remind yourself that you are an immortal being with more than five thousand years under your belt. That finally helps you to fully compose yourself, before you turn to walk away you look back at the girls eyes, so different and yet so strikingly similar to Costias. You nod at her and smile politely at her, she smirks in response and raises an eyebrow. If she knows who you are she's not letting on but she must. As you turn to go you see a name sprawled untidily across the bottom right corner of her pad, it reads Clarke Griffin. At that your heart clenches tightly in your chest. Although you don't need to breath you struggle to as you head to the alley way you can dematerialise in without being seen. Doing it in public causes too many questions.
You arrive back at your post not even a full moment later, that's all it takes for you to break down. You're a celestial being, you shouldn't be moved to tears by trivialities such as writing, but you are any way. The writing on the pad had been so familiar, it felt like only yesterday that you had seen it for the last time. That hair and those eyes combined with the writing left no doubt in your mind as to who the girl by the Seine had been. Costia had finally been reincarnated, after more than three centuries of you hopelessly waiting. Now after all of this time, you weren't ready. Clarke Griffin was your soul mate just as Costia had been, but she was just as much of a mortal as Costia had been. You aren't prepared to sit back and watch her wither away and die, from either disease or age, as you stay frozen in a time stream that doesn't effect you. You can't sit back and lose her again, even if you have more time by a few year this time.
The truth is, you're destined to love and to lose and so you'd rather not love a mortal at all. You would rather be destined to spend an eternity alone than go through with the inevitable. Although the pain will be unbearable for you, you know that given time and not a lot of it, you will go and seek out the reincarnation of your soul mate, because you have spent millennia alone and untouched by a world that worships and fears, and even a mere moment of warmth from the love of a mortal girl made the endless years of aching loneliness worth it.