Hundreds of years before the story of Inuaysha takes place, there was a priestess who spent her life fighting against demons, her name was Midoriko. When the nobles had all the power, for all the other people, it was just a cycle of war, famine and death. So, to feed on all the bodies of the dead there were more demons. Many monks and warlords could exterminate demons, but only one of them could extract a demon's soul and completely purify it, and that was the above mentioned Midoriko. She was so powerful that she could destoy ten demons at once. In fact she could not only extract there demon souls but the balance of four souls. According to the Shinto philosophy, all the world's creatures are made up of four souls (shikon). The four souls are known as arami-tama, nigimi-tama, kushimi-tama and sakimi-tama. Arami-tama resides over valor, nigimi-tama over harmony, kushimi-tama over miracles and sakimi-tama over love. Together, all the souls are housed in a phyisical body as the soul or "heart" (kokoro). A soul in which the four aspects are combined and balanced is called a naohi, which means true spirit. For a person who as all the aspects balanced, ti is easy to stay on the true path, but if a person commits an evil deed, then the aspects become unbalced and the soul is a magastuhi, or twisted spirit and that person would walk the wrong path. To sum it up, it means that a soul can become either good or evil. Now, to get back to Midoriko, Midoriko had the power to balance the four aspects and nullify the demon souls. Beacuse of that the demons feared Midoriko, and wanted her dead. But they knew that if they were to attack her outright, she would purify them and they would become nothing. So the demons decided to make a wicked soul that was so powerful, it could stand up to Midoriko. To do this, they found a man who secretly yearned after Midoriko and they all possessed him and became one. (This is acrually the same thing that happened with Naraku and Kikyou). When the demons and MIdoriko fought, the battle lasted for 7 days and 7 nights. But finally Midoriko reached the end of her strength and the demons devored her body. However, when her soul was about to be sucked out of her, she used the last of her powers to steal the demon's soul and take it into her own and push it out of her body. Then both the demon and Midoriko died, but they left behind a crystalized soul which is called the Shikon no Tama. It is said that inside the jewel Midoriko's soul and the demon's soul are still battling. So the jewel can be either good or evil. In the hands of a demon, it becomes corrupted, but in the hands of a pure-soul it becomes purified. So, over the hundreds of years it was passes between demons and humans of all different types until it finally made its way back to Sango's village where it originated. The way this came about is, Sango's grandfather fought a terrible demon and killed it. When he did that, the jewel came out of the demon's body. But it was horribly corrupted, so it was given to Kikyou to be purified. The jewel is surrounded by a cycle of life and death. Kikyou brought the jewel with her into death trying to end the cycle, but it returned with Kagome.