Tsubaki was a young miko (Shrine Maiden) in training, much like Kikyo had been in life. She served as an apprentice under a priest at a Shinto shrine. Tsubaki and Kikyo were rivals; although they sometimes fought side-by-side to defeat youkai, Tsubaki constantly tried to surpass Kikyo using her own holy power. While Kikyo and Kaede traveled through the countryside to visit small villages and help slay youkai, Tsubaki placed a curse on Kikyo. She told Kikyo that as a miko, she must abandon her heart, warning that if she ever fell in love with a man, she would lose her holy powers and suffer an untimely death. Kikyo responded with cool denial.
Spoiler
Tsubaki only places the curse on Kikyo in the anime.
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