Tsubaki

was the only seen dark priestess. She was the arch rival of Kikyō. Not wanting to get old, she desired beauty and made a deal with a demon, making her appear young. Unsurprisingly, she was manipulated by Naraku.

History
In her youth, Tsubaki was a gifted priestess; her talents were magnificent and she progressed quickly in her training. Tsubaki was seen as a high class priestess who was shown to have gained respect from other priestesses, even Kikyō; however, she saw Kikyō as a rival, as Kikyō's spiritual powers competed with hers, and she took many of the awards for slaying demons Kikyō had slain.

One day after Kikyō and Tsubaki helped out a village in slaying demons, Tsubaki subtly cursed Kikyō before she left. Disguising the curse as advice from one priestess to another, Tsubaki tells Kikyō that a priestess's true power comes alive when she abandons all human feelings, but if one is a woman, it's only natural to fall in love. Kikyō had scoffed at the idea of herself falling in love, but Tsubaki continued. Her eyes flashed red as she told Kikyō to not forget, and to never fall in love. If a man desired her and she desired him, she would die a violent death. Kikyō knew Tsubaki had placed a curse on her, but wasn't worried as she continued home. Tsubaki was triumphant.

Tsubaki feared that, with the passage of time her beauty would be gone, making her wish to keep the Shikon no Tama to prevent her own aging (which may be stated as the reason her master chose to give Kikyō the task to guard the jewel instead of her, because he knew Kikyō would never use the jewel for her own benefits).

When Kikyō was given the Sacred Jewel to guard, Tsubaki was jealous of Kikyō at having been given such an important task. Tsubaki confronted her master to inquire as to why Kikyō was given the Sacred Jewel to protect and not her, but Tsubaki's master didn't say anything. Tsubaki stormed off, leaving her master behind feeling sad for his disciple. It can be assumed that the reason why Tsubaki's master didn't tell her why she was given the jewel is because he didn't want to upset her, due to her heart not being pure enough.

During the season of spring, Tsubaki later confronted Kikyō in a forest and attempted to cast a curse on her using her Shikigami and then taking the Sacred Jewel for herself, thinking Kikyō's powers would be weakened after hearing of her infatuation with a half-demon. However, Kikyō used her bow to reflect the curse and sent it flying back at Tsubaki, which gave her a scar on her right eye. This caused Tsubaki to hunger for revenge on Kikyō, seeing her as a mortal enemy ever since. Somewhere between the past events and current events, Tsubaki made a deal with a demon and sold her soul to retain her youth and beauty.

During the story
Tsubaki is summoned by Naraku who knows of the dark priestess' powers. He recounts Tsubaki's tale of how she fought Kikyō fifty years prior and that she, Tsubaki, now holds a grudge against her. Naraku asks Tsubaki if she will help him in return for the, now nearly complete, Shikon no Tama. She accepts his proposal, as long as she gets the Sacred Jewel.

Tsubaki places a curse on Kagome with her Shikigami upon her return from the Bone-Eater's Well, needing some of her blood in order to achieve the curse. She forces Kagome to try to kill Inuyasha which causes Naraku to be amused with the irony of it. Inuyasha refuses to run away from Kagome though, and then Kikyō appears before Tsubaki. She warns Tsubaki that not only is Kagome more powerful than she appears, but if she did kill Inuyasha, she would avenge his death. Then Kikyō leaves. At the time, Kagome was snapped out of her trance and Inuyasha carries her to find the others who were trying to find the source of Kagome's curse. They all gather and confront Tsubaki after her barrier was destroyed. During her battle with Inuyasha, she threatens Inuyasha with Kagome's life, until Kagome attacks her with her sacred arrow; because of this Tsubaki begins to focus her attack on Kagome.

During battle, Tsubaki underestimated Kagome's skill and taunted her with the fact that her skills did not compare to those of Kikyō. Kagome, angered at always being compared to Kikyō and firmly stating that she is Kagome, uses her determined rage to withstand Tsubaki's painful curse and forces herself to move and attack her. In the end, Tsubaki was defeated by Kagome's spiritual power. Because Tsubaki underestimated Kagome's abilities, her curse was thrown back at her just like it was 50 years ago by Kikyō. With that, her control over Kagome was broken. In the manga, she isn't seen again.

In the anime, however, she managed to retrieve the Sacred Jewel used to control Kagome and made her escape. She appears later on and was able to escape to the shrine where she used to train. Tsubaki tricked the two priestess trainees, Momiji and Botan, into helping her fight Inuyasha, while she plans to awaken the sealed demon within a pagoda. She was told long ago by her master, never to unseal the demon. Kagura then appears to take back the Sacred Jewel, but Tsubaki refused to part with it. Kagura sticks around anyways, curious to see what would happen and to take back the jewel if Tsubaki fails. Tsubaki unlocked the seal that trapped the ogre demon in the Forbidden Tower, and to increase her power, absorbs the ogre. When Inuyasha and his group arrived, she transformed into a half-ogre form and attacked Inuyasha and the rest, however, in the end she was defeated by Inuyasha's Backlash Wave. During her attempt to use the Sacred Jewel before she died, a Saimyōshō emerges from her eye and takes the Sacred Jewel, thus taking her spiritual powers along with it. She wonders in despair about where she went wrong. Tsubaki's appearance begins to turn into her actual age. With her last breath, she regrets trusting Naraku, underestimating and losing to Inuyasha, and then she turns into dust as she shouts that she was the most powerful priestess.

Relationships
Tsubaki hated Kikyō and saw her as a rival. She found Kikyō to be smug and cold, and hated Kikyō because she thought Kikyō felt she was more superior. Tsubaki was jealous and desired the Sacred Jewel for herself. Tsubaki hated her to the point of wanting her to die and this continued even after she (Kikyō) was reborn. This conflict can be seen as one-sided, as Kikyō didn't express any anger toward her and was seen feeling sympathy for her when she died.
 * Kikyō

Due to Kagome being the reincarnation of Kikyō, Tsubaki despises Kagome and attempts to kill her just like she tried to do with Kikyō. However, despite the hatred she seemed to respect her power as with her dying breath, she said she regretted underestimating Kagome's ability.
 * Kagome

Tsubaki, despite being given the almost complete Sacred Jewel by Naraku, does not trust him that much. At first, she is impressed with his cruelty towards Inuyasha and Kagome, due to his plot forcing Kagome to try and kill Inuyasha like Kikyō did 50 years ago. But after her failure, she begins to realize she is just another pawn to him, and she begins to loathe him.
 * Naraku

Powers & Abilities
As a Priestess, Tsubaki had a range of spiritual powers and she was shown to be quite a powerful priestess in her youth. She was seen to have a high level of spiritual power when she easily broke the number of seals that was placed to trap the Ogre Demon created by Sages before her.
 * Shikigami - Tsubaki's proficiency in black magic comes in the form of summoning a demon puppet which appears as a serpent-like creature capable of cursing even the most pure of essences, such as tainting the Shikon Jewel and Kagome.
 * Sutra Magic - Tsubaki was seen to be able to use sutras.
 * Spiritual Power - Tsubaki's spiritual powers had once made her on par with her rival, Kikyō. However it had been diminished significantly when her Shikigami was reflected back at her.
 * Demon summoning - At the height of her black priestess power, Tsubaki had the ability to harbor a slew of demons in her cursed eye, all bound by her whims.

Manga vs. Anime

 * In the anime special, it was said that the reason why Kikyō lost her powers when she fell in love with Inuyasha (which wasn't mentioned in the manga) is because Tsubaki placed a curse on Kikyō.
 * In the Manga, Tsubaki does not die. She is simply defeated. This makes her one of the very few Inuyasha antagonists who survive in the series.
 * As it is mentioned in the synopsis above, Tsubaki's arc in the anime is quite extended from her arc in the original manga. The arc in the manga ends after Kagome reflects Tsubaki's curse back at her. In the anime however, the arc continues for a few more episodes, ending when she goes to the forbidden tower and uses the giant red ogre's power. In the manga, Naraku steals back the Shikon Jewel from Tsubaki when Kagome reflects the curse, but in the anime he lets her keep the jewel for a while longer, giving her the opportunity to exact her revenge.

Trivia

 * Tsubaki is the first and only dark priestess shown in InuYasha.
 * Tsubaki places a curse on Kikyō in the anime, Kikyō believes it is for if she fell in love. However, Tsubaki says, "Never let any man desire you or you are sure to die a violent death." This statement can be more attributed to Onigumo implying Tsubaki is the reason he came into Kikyō's life. Yet Tsubaki herself had no knowledge of Naraku nor Onigumo.