Soul marks exist in every species of the universe. No one knows how exactly they came to be because they had always been. Oh, many have tried looking into history, genetics, and even time itself, but the answer remains eternally evasive to even the most thorough of investigators.
Like many other things, the nature of these soul marks vary greatly from creature to creature. In a species of animal it might present itself in the pattern of their fur. In a species of plant it might present itself as a splash of color on a petal. In humans it takes the form of language, words that look around different parts of their bodies much like that of the animal’s fur pattern. For humans though, these patterns marked out an important word or series of words. It marked the first words they ever hear their soulmate say to them.
Time lords were similar but different than humans. Being a species raised in and around the time vortex, those from Gallifrey spanned across time and thus it would make sense that their soul marks did as well. For Gallifreyans and Time Lords the words that marked them were the first words that their soulmate would ever say to them, an important distinction developed by traversing non-linear timelines. A Time Lord could meet their soulmate and not hear the words etched into their skin only to run into a younger version of them who’d then utter each and every syllable. Because of it’s trans-linear nature, Gallifreyans as a whole make a practice of covering their soul marks.
Humans are similar in that respect as well. Because their soul marks are the first words they will ever hear their soulmate say, a trait that never had the need to develop the further distinction of those words being the first their soulmate might ever say to them due to the lack of proper time influence on their genetic coding, they cover up their words as as to prevent false positives from someone who might use them maliciously. In both species, sharing your soul mark with another was an incredibly intimate act and thus speaking of soul marks at all in public was considered taboo.
Those who knew about the series of elegantly arranged circles, lines, and dots scrawled across Rose Tyler’s left palm were few and far between; her mother, the doctor who recorded the etchings for her birth records, her friend Shareen, and one ex-boyfriend Jimmy Stone. Most would be surprised that Mickey Smith remained ignorant to the writing on his girlfriend’s hand, but while not content with the fact he was understanding of her hesitance, because above being her boyfriend he was her best friend. He’d held that hand through the good and the bad for the first nineteen years of her life.
For the first couple centuries of his life, the Doctor had no clue what the scribbles across his right palm meant. It wasn’t until years after entering the Academy that he learned of a small planet far off and full of uncivilized “apes” and their crude forms of language that he finally understood the origin of his soul mark. He finally understood the hushed way his parents argued about it behind closed doors as well. Humans were looked down upon by Gallifreyans, at best. At worst, they were considered no better than insects and to have one as a soulmate was unheard of.
He could have completely turned away from his human soulmate with the same disgust the rest of his species did, but instead they became another anchor through which his fascination with Earth and its people cemented itself in his hearts.
Rose Tyler met the Doctor after 19 years of life on the planet Earth. From the moment he whispered “Run” and slid his hand into hers, their soul marks pressing against each other through layers of fabric, a sense of rightness settled itself in her life. Through running, and danger, and near death experiences she had zero regrets because somehow she knew this was where she was meant to be. In the entirety of the universe, it was by the Doctor’s side that she felt the most belonging.
There was one moment in between the hustle and bustle of adventure, a moment of relaxation and rest floating through the vortex, when Rose asked her Doctor what the gold writing across her door meant. He sensed it was important to her, though he didn’t know why.
She held her left hand over her heart as he told her it was her name written in Gallifreyan.
Years of adventure, and years of excitement, and years of running accumulate to a moment of devastating heartbreak punctuated by a name trailing off into the wind as the image of a century old alien fades away on a nearly empty beach in Norway, and then again on that same beach years later in the presence of the same man who isn’t actually the same man.
The not-same man who finally give her a tentative explanation for the words on her left hand when he explained the differences between the soul marks of the human and gallifreyan species. The not-same man whose right hand remained blank.
Far away, across multiple universes, the Doctor would often stare at the words across his palm and let himself grieve for both the one he lost and the one he had yet to gain, because the haze of grief had him wondering how he could love a soulmate after losing the love that most fulfilled his soul.
He turned fully against the teachings of his people, fighting against the very laws of time in his downward spiral after losing everything; not just Rose, but every companion before and after the Time War. His song was ending, or so he’d been told, and in his last moments as that him he went back to see the most important face to that face and to the face to come.
He’d meant to stay in the shadows, for her not to notice him through the haze of the New Years snow on her way back to her home on the Powell Estate, but a surge of pain from holding back the regeneration energy for so long caused him to cry out - not loudly, but loud enough to turn that head of bottle blonde hair his way.
“You alright, mate?”
The pain in his body was nothing compared to the pain clustered in his heart in time with the warming of his palm.
“Too much to drink?”
He pulled his right hand against his chest - the hand with his soul mark etched across his palm. Not the first words he’d hear, but the first words she would ever say to him.
“Something like that, yeah.”
Years later, with a different face but the same heart, a man with floppy hair and a bow tie visits and infant girl with eyes wide open despite the late hour and staring at the stars spinning on the mobile above her bassinet.
He smiles sadly at her apparent fascination with the stars even at such a young age. The ache was still there, pulsating under the half-mad antics of a raggedy man.
He reached out and nudged the mobile to move just a smidge faster to give the child that would grow into the woman whose hand fit perfectly into his a taste of the vastness, the intensity, of the universe.
He sighed, drawing those tiny, twinkly hazel eyes away from the mobile. She reached out to him, her hands grasping into space, and he gave her a finger to cling onto with her tiny appendages.
The warmth of affection briefly overpowered the ache of loss, but he couldn’t let all of that distract him. He’d come here with a purpose, one that he’d long put off but knew was necessary.
He needed to speak his words; not the first words he would ever say to her but the first words she would ever hear him say; words that he tried to say once, long ago, on a beach in a distant universe; words that he saw for the first time etched across her infant palm in circular Gallifreyan when her hands pulled away in surprise as he felt them warm in time with the syllables escaping his lips for the first and last time.
“Rose Tyler, I love you.”