(From Wikia):

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Kikyō (桔梗, "Chinese Bellflower") was a miko during the Sengoku jidai and, at one time, Inuyasha's main love interest. She was entrusted by the yōkai taijiya to guard and purify the Shikon no Tama. Along with her younger sister, Kaede, Kikyō dedicated her life to protecting the jewel, slaying many demons in the process and thus could not live a normal life like other girls. It was not long until she met the hanyō Inuyasha, who also desired the mystical Jewel to become a full-fledged yōkai. Somehow, she sees him as a companion and desires to live a normal life with him. However, fate turns cruel against her when Naraku, a hanyō that coveted the Shikon no Tama, tricks them both into betraying each other. When she is led to believe that Inuyasha wanted nothing but the jewel, she seals him to the Goshinboku and dies a painful death. Before dying, she asks her younger sister, Kaede, to burn the jewel along with her body so that it would not fall into the hands of evil again.

Fifty years after the incident, she is resurrected by the demon ogress Urasue, using grave soil and the soul of her reincarnation, Kagome Higurashi. Shortly after, Kagome calls her soul back and Kikyō is forced to rely on the souls of the dead, collected by her shinidamachū, to sustain her fake body. Though she was initially cold-hearted and harbored deep hatred towards Inuyasha, this hostility gradually disappears and her love for Inuyasha returns. As she is already dead, she resolves to not rekindle her relationship with Inuyasha and pours all of her resources into helping others, destroying Naraku and purging the Shikon no Tama from the world. In the end, however, Naraku's darkness proves too powerful and overcomes Kikyō's power, completely corrupting the jewel. He strikes her down, wounding her fatally. After sharing one last kiss together with Inuyasha, her soul finally finds peace and her body disappears into a bright cluster of souls and light. The shinidamachū then carries Kikyō's soul into the star-filled sky.