A long time ago, before Kikyo's existence, Inuyasha and Sesshomaru have been rivals since a young age. Their rivalry started and carried on because of the Shikon no Tama's Goddess.
The story of the Shikon no Tama:
Long ago, a young goddess named Sayomi was a powerful goddess, and was able to create miracles such as intensive healing abilities that exceeded any priestess or demon. She was also a goddess of destruction, with skills powerful enough to kill almost any demon or god that stood in her way. One day she encountered a small boy who pleaded to for help. He was missing an arm, and having heard about her abilities, demanded that she regenerate that arm for him. She sensed an aura that wasn't of a little boy, so she refused. After refusing three times, the boy's body turned into the god of revenge, who disguised himself as a young boy, creating scenarios in order to take revenge as his entertainment. As he was one god that was more powerful than Sayomi, he made a copy of her powers and stored them inside the jewel, known as the Shikon no Tama, and trapped her in a human body of a young but powerful priestess as a curse. The only way to trigger her goddess powers is when she is unconscious, and her subconscious mind will surface, and after this the god of revenge vanished. He made sure to hide the Shikon no Tama somewhere far away, forcing Sayomi to search for it so that she can reunite and become a full goddess again. To add to the curse, the god of revenge took away most of her memory of being a goddess, having her only being aware that she had to find the Shikon no Tama.
Sayomi spent a few years wondering around in search of the Shikon no Tama but also helping people along the way. Because she was in her human form, she attracted demons and was prone to clumsiness, caused by the Shikon no Tama aura she gave out. She performed many healing rituals on villagers and helped exterminate demons with simple priestess powers, which gave her clues as to where the Shikon no Tama was hidden, and then she met Inuyasha.
Sayomi's Description: Long black hair, slightly wavy, side bangs. Her hair is sometimes tied up into a high ponytail, with a slight curve. She wears a kimono cut short at her mid-thighs to move around easier, and she wears fur boots like Koga's.