There once was a very powerful priestess with flowing blond hair and forest green eyes. Her name was Sakina. Sakina protected a village on the eastern coast of China. When she was 20 years old a fire demon sent for her. He said that she must go to the cliff outside the village or he would destroy it. To protect her village she went. At least that is what the village was told. Sakina may have been a priestess, but she was still a female. Akir, the fire demon, was handsome. He was muscular and tanned. He had short, spiky, bright red hair, deep blue eyes (like the center of a flame) and wore only loose black pants with a gold sash around his waist. She fell in love with him, and he with her.
Eventually the village found out. Sakina was pregnant and was exiled from her village. Akir told her of an island off the coast of Japan that could be safe for her called Hourai Island. He promised to join her there before the child's birth. To protect her he gave her a kimono made from the fur of a fire rat and dyed black.
The journey to Japan took six months, and she spent another month trying to find the island. She couldn't find it, but she found something else. Sakina found a woman in the same predicament as she was. Izayoi was a noble woman who had a baby boy, InuYasha. He was only a few months old. Three months after meeting her Sakina gave birth on the new moon to a baby girl. She named her Akasha. Akasha had the same bright red hair and blue flame eyes as her father, that is until the full moon. Then her hair lightened to blond and her eyes darkened to green.
Years went by; Izayoi got very ill and made Sakina promise to care for InuYasha after her death. Sakina, being a loyal and grateful friend, did and a few days later Izayoi died.
InuYasha and Akasha were raised as brother and sister and acted as such. They made a pact that they would always protect each other at their weak points (for InuYasha the new moon, and for Akasha the full moon and the winter solstice).
Sakina lived to a surprisingly old age and was buried next to Izayoi at her request. InuYasha and Akasha couldn't stay at the temple anymore. So, they roamed Japan.
Eventually they learned of the Shikon Jewel. InuYasha wanted to become full demon. Akasha didn't care either way, she knew her strengths and weaknesses and was happy with it. So they went in search of the Jewel. Upon finding it they also found Kikyo. Akasha sensed Kikyo would develop feelings for InuYasha and tried to dissuade him of going after the Jewel. Akasha knew it would end in heartbreak so she left.
Meanwhile, Akir left China two weeks after Sakina. He got information about her but was always just behind. Many of his tribe joined him in his search. Akir was in the process of searching when Inutaisho (InuYasha's father) stopped him. In return for allowing Akir and his tribe to live on his lands he was given a red kimono made from the fur of a fire rat. (Which he later gave to Izayoi.)
Akir didn't find Sakina until after her death. No one would tell him of his child. All he knew was that it was alive somewhere and he swore to find it.
InuYasha was pinned to the tree by Kikyo. Kikyo died shortly after and took the Jewel with her to the other world. Akasha returned, but she was too late to do anything. She stayed in the village for a short time helping where she could, but she didn't stay long.
During the next 50 years Akasha came to acquire a pair of swords called "The swords of Kuijin." These blades could create three battle moves she couldn't use otherwise. She wasn't around until after InuYasha was freed and met Kagome, Miroku, and Sango.