"Lord Sesshomaru, how old are you?" Rin asked the night he had given up his immortality.
"One thousand three hundred and sixty nine," he answered steadily while he examined his claws. He felt different. He no longer felt his age, he felt very much alive and powerful, though he had always been both those things. The feeling confused him greatly.
"Are you going to keep counting from there?"
"What else would I do?"
"You could count in human years. If I were to guess how old you look I'd say..." Rin examined him with a careful eye before nodding. "Nineteen. Milord, you look nineteen to me and that's perfect because you'll still always be older."
"You no longer need to call me 'lord'," the taiyoukai said absently as his eyes found the looking glass in her room. Nineteen? That was a toddler to youkai. "Alright, nineteen it is."
Sesshomaru held one of the small pups the miko Kagome handed him while Rin took the other. Light as a feather he brushed his finger on his son's cheek stripes, so like his father's.
"They both look like you," Rin whispered. He could smell her exhaustion, but also her joy. With a smile she showed him the tiny girl and her crescent moon marked forehead. Both his children had his pointed ears and markings, but he could already tell that despite their golden colour they had his mate's eyes and both twins had little tufts of black hair.
Sesshomaru watched the twins, Tsukiko and Asahi, practice their swords, though he could tell they had slowly fallen into playing. He couldn't believe they were ten already. His hanyou grew at the same rate the local human children did, but Inuyasha assured him once they hit their teens their youkai blood would begin to take effect.
He shifted the weight in his arms to a more comfortable position. His little girl, six years old, had fallen asleep after her lesson.
She was the spitting image of Rin, her face was so like her mother's had been when he first found her. Nariko resembled her uncle a fair bit though. Perched atop her silver hair were puppy ears.
He felt as though time sped by too quickly, he wasn't accustomed to how fast changes occurred. His appearance shifted far too quickly as did those around him. All five of his pups had hit their teens and just as Inuyasha had said their aging slowed down greatly.
The changes in himself were even worse. After centuries of looking no older than his teens the taiyoukai had a few wrinkles around his eyes. Sesshomaru frowned at his reflection when Rin joined him.
"If you keep frowning you'll just get more you know. You're so vain, you're only forty three," she teased as she fixed her hair. Sesshomaru ran his fingers through the loose strands. Her dark hair had begun to change over the years, a good portion was as silvery as his own.
He gently kissed her forehead, he still didn't like how fast time went, but he was getting better at appreciating every breath he took for what it was; another day with Rin.
His youngest son mated with a human girl. When Dachi handed him the small baby girl she barely smelled of youkai.
"You're a grandfather now, Old Man," Inuyasha said as they walked the path to their respective homes.
"And you will be one soon too, Little Brother."
His mate of fifty years lay in bed, facing an adversary he had never been able to stop; time.
"Stay with me, Rin," he whispered, her hand clasped tightly within his own.
"Death isn't so scary, at least this time I've lived my life," she said weakly with a smile. "I'll wait for you."
Time had gone by so fast, even with him giving up his longevity he still lost her. Running his claws through her snowy hair he thanked his ancestors that he had learned to take the time to enjoy the little things.
This time, he hadn't blinked.
So for those who are curious Rin and Sesshomaru had five kids, Tsukiko & Asahi, Nariko, Daijiro & Dachi. Two girls and three boys with two sets of twins. Daijiro and Dachi have silver hair and golden eyes, aside from that they look human.
I had an alternate, or rather extended ending that I'll put here.
Sesshomaru slowly drifted to sleep, alone in their bed, as his memories turned into dreams.
Rin sat under the tree they had first met, for a moment she looked eight years old and was wearing the familiar orange and yellow kimono he gave her. She turned and smiled, a bouquet of flowers in her hand.
"Lord Sesshomaru!" As she stood she grew, became the woman he had mated eighteen again. Looking down at his own hands he saw they were no longer knarled, but smooth. "I waited for you," she said as she gave him the flowers.
"I'm sorry I made you wait, you weren;t supposed to." He looked at the flowers, their smell was sweet like the millions of flowers she had given him over the years... Wait. Smell? He looked at her questioningly, he shouldn;t be able to smell in dreams. She smiled and pulled him into a hug.
"It's okay, it was only a year."
So yeah, just a small little add on. Sesshomaru passed away peacefully in his sleep a year after Rin died, he didn't have to live long without her.