Because Kikyou was burdened with protecting the jewel she lived a lonely existence. She turns to InuYasha, explaining that if he were to use the jewel to become a human instead, the jewel would be purified, and disappear. She would be released of her obligation and they would be free to be together. InuYasha agrees, and they plan to meet the next day.
Their plans are foiled, however, by Naraku, a half demon who was once a man named Onigumo. He lusted after Kikyou, but when she does not return his affections he allows demons to take over his body, and thus Naraku is born. Naraku wishes to taint the jewel, so he disguises himself as InuYasha and attacks Kikyou, stealing the Shikon-no-Tama. He then returns the jewel to the temple, disguises himself as Kikyou, and attacks InuYasha. Thinking Kikyou has betrayed him, InuYasha steals the jewel from the temple. However, Kikyou manages to track him down and with the last of her strength she seals InuYasha to a tree with her sacred arrows. She dies from the wounds Naraku inflicted on her, and she has the jewel burned with her body.
InuYasha remained sealed to the tree for 50 years, until one day 15 year old Kagome Higurashi falls down the well at her family shrine, travelling to feudal Japan, about 500 years in the past. She is able to awaken InuYasha, who originally mistakes her for Kikyou. It is later discovered that she is in fact the reincarnation of Kikyou. The sacred jewel is discovered inside her body, but it is removed by a demon called Mistress Centipede. The jewel is eventually shattered by one of Kagome's arrows, so she agrees to help InuYasha locate the shards.
At first InuYasha is reluctant to get close to Kagome. He still feels betrayed by Kikyou, so he does not fully trust Kagome. However, as their journey continues, and the truth about Kikyou and Naraku is revealed InuYasha begins to trust Kagome, and a friendship develops. The two become very close, and Kagome soon falls for InuYasha.
Their relationship is not simple, however. Many people try to interfere, including a wolf-demon named Kouga, who is in love with Kagome. InuYasha is very jealous, afraid Kagome may one day return his affections. But perhaps the greatest interference is Kikyou, who's body is later resurected. Because her soul was reincarnated in Kagome, she is only a shell of her former self, forever trapped with the anger and hatred she felt when she died. She does, however, still have feelings for InuYasha but she realizes they can never have a future together. Kikyou now plans to kill Naraku, so her soul can finally be at peace.
While InuYasha has genuine feelings for Kagome, he is still confused by his feelings for Kikyou, and their relationship is often put on hold so he can sort them out. Unlike Kikyou, however, Kagome has no desire to change InuYasha. She does not want him to use the jewel to become a human; she loves him exactly the way he is, as a half-demon. As the series progresses, InuYasha slowly allows his feelings for Kagome to show. He eventually comes to realize that Kagome is the one he truly wants, though he is often reluctant to admit it.
