Mortality is his biggest nemesis now, Sesshomaru knew.
Demons are not immortals. They are born, the age, they die - the same way the rest of the world does, but time for these otherworldly creatures simply don't tick quite the same as it does for the rest of the living. Weeks pass like hours and years like days. Time seemed always at a standstill.
But for humans? No... Humans are different. To them, time is everything. Every breath, every second, and every minute counts. There isn't a moment to waste for humanity only had so little. They remain young and youthful for what felt like only weeks to demons, and Sesshomaru, the Great Demon Lord of the West, feared the power of time - not for his own mortality, for hers... for Rin.
The final battle for the Shikon no Tama had long been over. Peace had been restored and the balance of chaos and serenity had been brought back by the priestess Inuyasha had wedded soon after she returned to their time. The demon lord used up that time to further expand his territory - to strike fear in his rival's souls, all while Rin grew up in beautiful fields of her human village, blossoming to be a beautiful maiden who captured the heart of many. Of course, he came back for her. He always planned to.
Beautiful was an understatement in describing her. She was taller than most, with a slender physique and a toned build that outlined every crease of her body. Her hair was dark as ebony - long, shiny, and soft - comparable only to the purest and highest quality silk ever made. Her lips - the one part of her that caught his eye too many times to count - were full and red; a perfect, natural color unlike no other. Her eyes were big, bright and innocent, and they never failed to look at his own with a look that convinced him she had the whole galaxy trapped behind those shiny brown eyes.
Their first night together was his undoing. It was taboo - unnatural and dangerous - and yet, it was bliss. Her scent filled his lungs as he breathed in her aroma - one that smelled a lot like fresh roses. Her naked body against his very own was warm and soft, yet firm and strong all at once. Her perfectly toned build outlined every crease on her arched back, and he watched in fascination as beads of sweat rolled down her flawless skin, baked to a perfect color under the heat of the sun. Her voice - oh, her voice - was music to his ears. The melody of her moans and her high-pitched gasps were his new addictions. He craved the primal moments when she'd dig her nails into his skin, clawing on his back in desperate attempts to hold him closer - tighter - leaving marks on him that he secretly wished would have lasted much longer. But his favorite part was at the end of it all, when she lay asleep on his chest and she could hear every breath she took and feel every beat of her heart pulsing against his bare skin. The moonlight reflected on her gracefully and he wished time would have just stood still then. This was his innermost desire; his darkest fantasies, and he's living it. And for the first time in his life, time felt like it moved far too fast.
She was much like an addictive drug - he knew from the moment he saw her again in all her prime and glory that this is how he'll fall, much like his father before him.
He spent most of his days watching her, even when she didn't know. He came to see her almost every day after, though, for most of those times, she didn't exactly saw him back. He was conflicted - the turmoil in his heart burned hot and for the first time ever, Lord Sesshomaru didn't know what to do. Jakken's insensitive commentaries only made his anxious heart fear more; Rin was human, and him, a demon. She will grow old and weary and pass away and Sesshomaru will remain untouched by time through it all, young, beautiful, and mournful as he watches the woman he loves age and and die, leaving him behind.
What was father thinking?, he thought. The Great Demon Lord before him had given his heart to a human - surely, he must have known the inevitable end of that story, had he not been killed before his human wife passed her prime. Did he have a plan? Did he somehow had a way to save her from her mortality and give her the lifespan of a demon? Is such a feat even possible?
For the weeks after, he spent his days searching and his nights in bed with Rin. He wanted to savor the moments as much as she would allow him to; he ravaged and took her, over and over again each night. He craved her - not just her body, but her as a whole. He craved her smiles, the sound of her laughter, her terrible jokes with references he never understood, the way she flusters - never seeming to get used to seeing his naked body in the daylight after a busy night spent in his arms, the way she looks at him like he's the only thing that mattered in her world, the way her hair blows in wind, the way she skips around when she's happy, how she prefers to eat with her hands instead of utensils. He could sit there all day, naming every detail about her that plays a part on why he could never seem to get her out of his head and he still would have more left to say. He loved her - and while he's yet to form the courage to admit that to her, he knew she knew. She always seemed to know what he was thinking without having to say much.
He used his influence and his power to dig deeper, ignoring the protests of his subordinates. Word spread fast and demons in all regions had began catching the rumors behind the silver-haired demon's actions. A human woman, they say. Just like his father before him. But Sesshomaru no longer cared - he only wanted to be with Rin.
But alas, his search was futile. No magic, outside the impossibilities of the Shikon no Tama, has the power to give humans more time. It just wasn't how things were meant to work. Humans are fragile creatures and will forever remain to be.
The night with Rin after that discovery was far from their ordinary. He held her in his arms far much longer than he intended, but he couldn't to let go. The thought of having to live without her in what would feel to him like the near future was unbearable. But Rin - all these time, she's never known what he had been up to. She didn't know what'causing him turmoil. She couldn't understand what's hurting him like this, and so she can only do what she knew best: to be with him. Wrapping her arms tightly around his waist, she held him even closer, hoping the proximity would at least ease his troubled mind.
After what felt like an eternity, he finally spoke.
"I love you, Rin."
She knew before, of course, but hearing the prideful demon lord admit to the biggest taboo of his kind was something she did not expect. What felt like a thousand butterflies crowded in her stomach as she buried her face against his chest with joyful, teary eyes.
"I love you too."
He stayed there for the rest of the night under the dark shroud of the new moon, locked in her embrace.
The commotion his search for the Fountain of Life had caused a stir among the demon population. It garnered interests far and wide and even those uninterested in demon politics had their interests piqued for curiosity reasons. True, the merger of a human and a demon is taboo, but it happens often enough that there's a market for a cure for mortality that would allow these unions to be in the same platform. To be one to find a solution meant raising up the demon hierarchy and having their names etched in both demon and human history, and so the real search began.
Only days after Sesshomaru's heartfelt confession did he get a visit from an unnamed visitor. An old woman - seemingly a witch - that knew his father came to him in the dead of the night, cloaked in a veil that looked darker than black. She was bony and short, and her skin looked like it was pasted onto her bones with no flesh in between. Her breath smelled like decay, an even from a couple yards away, her stench was apparent, especially to a demon's senses. Her hair was long, scarce, and dry - white like bone, and the strands seemed to have a yellowed tip. She, however, walked surprisingly upright, and her eyes, dark as the night, had a certain glow in them that looks almost... young.
She came to offer him a deal... And without much thought, he accepted.
The sun felt like it was scorching his skin by the time he woke up. Bright. Almost too bright. Looking around, it seemed to be almost noon.
Sesshomaru sat up from the grass in which he slept - he didn't remember sleeping, but that was the last of his worries right now. He felt sick - a feeling he was not familiar of. His throat felt dry like he hadn't drank in over a century. His body felt heavy and the fur scarf that was his signature attire felt even heavier. Standing up, the ground felt uneven, and his senses felt dull. Aimlessly, he listened for the sound of running water. He wasn't that far off from his brother's village where Rin lived, so he knew the terrain pretty well, even without the help of his superb senses. Perhaps a drink would make the ordeal more tolerable.
Upon reaching the river just above the town line, he could barely recognize his own reflection.
His once silver hair had turned black. The markings that was the birthmark of a demon lord was nowhere to be seen, and his signature claws were replaced by fragile human nails. It was a fascinating change; one he did not expect but was within the scopes of his understanding.
After taking a long sip of water, he made his way down to the village.
The townspeople watched him in a mix of awe and aghast. They recognize him; they knew him. And while they knew of the infamous Lord Sesshomaru that protected their town in favor of Rin, they had known him as the silver-haired devil that once overpowered and vanquished the power of a famous monk. He was a demon lord, one of the most powerful ones, and yet he walks among them now, clod in the body of a mortal.
The murmurs of the village reached Rin in mere minutes, and she ran to him, along with Inuyasha and his wife, Kagome. And just like his half-brother and his priestess wife, the woman he loves is speechless. She stopped short mid-run, staring at him with wide eyes and for a moment, he feared she would reject him. Was the change too much? What if she only loved him because he was a demon? In mere seconds, he was overwhelmed with doubt, but it was cut short as Rin jumped into his arms with an intensity he's never seen before. And she just held him there, their solemn silence shared amongst the village bystanders that watched the dramatic ordeal.
Finally, Inuyasha's voice broke the heavy air, bringing up the question everyone's been meaning to ask:
"What did you do...?"
Rin lifted her face from his chest, looking up at his golden eyes with an expectant face. She too, wants to know. And so he told her.
The merger of a human and a demon will always be taboo. They are two world never meant to be together. But sometimes, love transcends that law.
Inu no Taishou had planned it all along, back when he fell for his human wife. He would have long outlived her, and he didn't want to. He wanted to grow old with her and raise their child together, and he had planned to live through that plan after the war, had he came back from it alive, but alas, he didn't. Humans can never extend their lives and demons cannot shorten theirs... unless a trade is made. For a human to gain mortality, they must perform a fair trade with a demon and live out that demon's lifespan - in exchange, that demon lives a human life. The exchange has to be done willingly, as was the law of nature's balance. But to human's disadvantage, demons looking to be humans were scarce. Inu no Taishou had agreed to trade his with a witch's, one who craved immortality, in return for the ability to live a mortal life with his family. But the deal fell through when the old demon was killed and the witch retreated, on the verge of using up the rest of her remaining life force until Sesshomaru came along.
He had traded his demon blood for mortality, a price he was more than willing to pay for the one he loves.
Finally, he could be with her forever.