She had come back through the well when she was 18 and had become his mate in the tradition of his clan. They stayed in Edo, building a hut not far from the old miko's hut. He had made sure to build near the hot springs as well, keeping in mind her incessant need to bathe. She had studied under the old miko in preparation for her passing, collecting herbs, healing the sick, setting bones and birthing babies.
The monk and slayer had stayed in Edo, the monk overtaking the position of village priest after the previous priest had passed on. Their hut was built near the old miko's as well so the monk could easily be of service to her. Their children had been born and raised in Edo, playing with the other children of the village. They had taken husbands and wives and built their own huts in the village, staying near their aging parents and overtaking their responsibilities as their own, continuing the tradition of slayers and monk.
His own children had been born more human than hanyou and aged as she had. They were accepted in Edo and had happy childhoods with the other village children. They, too, had taken their own husbands and wives, built their own huts in Edo, and stayed close to their parents, continuing the tradition of mikos and village protectors. The kit came back to visit always considering them his parents, however he spent more and more time with his own kind, taking a mate and raising his own family; exactly as it should have been.
She had aged, as she was meant to. As the years passed, she grew older, she wrinkled and grayed. She was never more beautiful to him. He aged as well but due to his demon blood not as quickly as she. It was obvious he would outlive her by hundreds of years and there was no way to change that. No demon magic to bind her lifespan to his. No wishes to make him human. They lived her life together as they had been when she came through the well: a human and a hanyou.
He had made arrangements with the monk and his brother, acting as his kaizoe, in advance for the ceremony he had planned for himself. With his formal robes on, his haired bound at the nape of his neck and resting over his right shoulder, he kneeled under Goshinboku. His wakizashi, crafted specifically for this occasion, laid before him, his brother on his left, the monk on his right. He took in a deep breath and looked up into the branches of Goshinboku, smiling and soothed for the first time in years. He knew she never would have agreed to this, but felt under the circumstances she would have supported him had she known. The life he had after her was so much worse than the life he had before her because now he knew the difference.
He handed his poem to the monk, opened his kimono and took up his wakizashi in both hands. With a deep breath he plunged the wakizashi deep into his abdomen, moving it from left to right. On the upstroke, his brother brought down his sword, severing his neck with the exception of a piece of skin to keep his head attached to his body. As the hanyou fell, the monk said a prayer for his soul.
His brother prepared his body, washing his beautiful, silver hair and dressing him as was customary for his station as a Lord. Once he was cremated his ashes were entered into a small shrine next to hers under Goshinboku and InuYasha and Kagome were finally together again.