Inu-Yasha What happened to Kikyo?

Ok, every time I read about Kikyo it says she died after she sealed Inuyahsa to the tree due to an injery. Well, what injury, and how did she get it? I missed the first episode...

 

Spoiler

They dont tell you how did she get her injury in the first episode. I believe it was in the 21 episode when Naraku first appeared. He told Inuyahsa and the gang about what he have done to 50 years ago (the day where Inuyasha got sealed by Kikyo). Naraku is a shapeshifter! He turned to Inuyasha's form and attacked Kikyo telling her that he doesnt have any intention of using the Shikon's power to turn into a "pathetic" human. He told her that he acted as if he loved Kikyo to get the Shikon shard. She used her last strenght by sealing Inuyahsa on that tree.
All in all, she got the injury from Naraku who was in the form of Inuyasha!
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