This woman, whose name was never revealed in the series, fell in love with Raizen and bore him a child. She and Raizen are Yusuke Urameshi's ancestors. She is voiced by Colleen Clinkenbeard in the FUNimation dub and by Mika Doi in the Japanese dub.
Raizen's lover had long dark hair, blue eyes and pale skin. She wore a dark-blue kimono with an obi sash. Raizen describes her as "the most beautiful creature he had ever seen." She possessed a very curvy, feminine figure.
While only her insides and blood are corrupted in the anime, in the manga Raizen sees that the rotting flesh she ate has taken its toll on her body, as her flesh seems to be rotting and corrupt as well, making it much more threatening in the manga.
She heals Raizen after he sustained injuries while on a raid in a Human village. Through this interaction, the two eventually fell in love with each other. Because of her, Raizen swore to never feed on humans again, and thus began to slowly starve to death over centuries.
She had a temper, but was also apparently very intelligent. Raizen says that Yusuke has demonstrated her fiery temper.
700 years ago, in her time, the human world was a very different place. The kekai barrier had not yet been erected, and there was chaos and disorder throughout the land. The humans of the time were in constant fear as they lived side-by-side with demons, and the daimyō weren't above contracting their help in order to defend their territories from rivals and enemies. Raizen explained that at that time in his life, he was particularly uncaring because he saw all humans as food.
He then talked to Yusuke about how he couldn't find it in himself to care that in her eyes, he could see his downfall; he had fallen in love. He then goes on to talk about how she was a medicine woman and healer at the time, being an esoteric Buddhist doctor who practiced medicine by ingesting deadly poisons and contagions in order to turn her own blood into primitive vaccines. Her techniques were surprisingly effective, and his wounds healed quickly.
When the woman fell asleep, Raizen began thinking about how to eat her. The woman woke up and taunted Raizen, stating he may eat her, but that her flesh and blood turned toxic and polluted enough over the years in her tenure to kill him, and that he'd better hurry up with whatever he ended up doing. Raizen was mesmerized by her fearlessness, and the two of them ended up making love.
In the morning, however, Raizen left after realizing that he wasn't worthy of her. His reasoning was that she had devoted her life to saving people, while his life had been nothing but destruction, and vowed to never eat another human being until he saw her again. Unfortunately, he was never to see her again, as she died in childbirth.
Raizen spent years searching for her reincarnation, but ultimately realized that she was far too enlightened to be brought back to this world. Before his death, he stated that he hoped to be reunited with her in the next life.