Doppelganger (novel)

"When a witch is born, a doppelganger is created. For the witch to master her powers, the twin must be killed. But what happens when the doppelganger survives?"

Mirage is a Hunter, a trained spy and assassin, and she is Very Good at what she does. Miryo is a sorceress--or about to be one, as soon as she passes her initiation test. But when she is finally given magical power, she can't control it. Her other half, Mirage, is still out there somewhere, a part of her that can't be focused on the magic. In order to ensure control of her powers, Miryo must track the Hunter down and kill her. But how can you kill someone who is one half of yourself?

The two books in this duology by Marie Brennan were originally titled Doppelganger and Warrior and Witch. They've since been retitled as simply Warrior and Witch, but are still referred to as "the Doppelganger series".

Tropes used in Doppelganger (novel) include:

Action Girl: Mirage, and later Mirei.
Anti-Hero: Satomi in Witch. She lies, cheats, generally manipulates the hell out of people, and trusts no one with the whole truth of anything, yet her motivations are ultimately for the good. To her, the ends justify the means.
Badass: Mirage and Eclipse. Later also Satomi, Ashin, and Mirei. Amas, Lehant, and Indera are badasses-in-training.
The Bechdel Test: This series contains exactly two male characters of any importance, one of whom appears in only a handful of scenes. Needless to say, it passes with flying colors. In fact, you'd be hard pressed to find an incidence of it passing a reverse Bechdel Test, given that Eclipse and Jaguar spend most of their scenes together talking about Mirage, the witches, or Mirei.
Big Good: Satomi in Witch...for some value of "good".
Blonde Guys Are Evil: Eclipse averts this trope hardcore.
Blood Oath: Mirage and Eclipse take one at the beginning of Warrior. At the beginning of Witch, Eclipse is forced to take another one to kill Mirei. He'd never actually do it, of course, and Mirei spends a large portion of the rest of the book trying to figure out how to get him out of it before he dies himself.
Cacophony Cover-Up: At the end of the first book, Mirei uses the cover of applause to knock out a couple guards on her way to confront the Primes.
Can't Live Without You: Inverted. Unless one kills the other, neither a witch nor her doppelganger can die if the other is still alive.
Divine Intervention: Several times. Afterward, the characters tend to cogitate on the nature of the Goddess and why it took her so long, anyway.
Elemental Powers: Magic is based on the four elements: Earth, Water, Air, Fire. There is a fifth element, Void, which is important in other aspects of religion and society but has no magic associated with it. Or so they think.
Evil Redhead: Shimi, Arinei
Executive Meddling: The replacement of the original titles with the much less appropriate new titles.
Face Heel Turn: Arinei, but you saw it coming a mile away.
Fantastic Honorifics: Sixteen of them, based on rank.
Fiery Redhead: Mirage, and to a lesser extent Mirei.
Good Is Not Nice: Satomi after her Heel Face Turn. Probably Mirage too--she's definitely not someone you'd want to run into in a dark alley.
Heel Face Turn: Satomi after she learned the truth about Doppelgangers. Also Kekkai after Satomi tells her that the Primes had her predecessor killed.
Heroic BSOD: Miryo, after killing the Cousins to escape the house where she was being imprisoned. Also Mirei temporarily, when Satomi tells her that Eikyo has supposedly become a Cousin. Even later, Indera has one after she kills Sharyo.
Heroic Sacrifice:
- Ashin is prepared to do this when she and Mirei go to rescue Kekkai. She does.
- Later, Mirei and Eclipse both try to do this to save the other from dying. Fortunately, the Goddess takes pity on them.
Hero Worshipper: Deconstructed/subverted/something with Indera, who first wants to be just like Mirage and thinks she can do no wrong. But after she finds out about Mirei being a witch and the fact that Mirage as such no longer exists, she feels that Mirage has betrayed her and refuses to stay in her presence. This causes more than a few problems.
Like Brother and Sister: It is stated that Mirage and Eclipse feel this way about each other. At the end of Witch, however, it is implied that Mirei and Eclipse aren't inhibited by such things.
Magic Music: all spells are sung, and all witches get extensive voice training.
The Mole: Tajio in Witch.
My God, What Have I Done?: Satomi in Warrior, when she realizes what Mirei's very existence means about her past actions. In Witch, Indera after being brainwashed into killing Sharyo.
Only Known by Their Nickname/ Red Baron: Hunters. They have names like Mirage, Eclipse, Jaguar, Avalanche, Ice, and Talon. They discontinue use of their birth names upon graduating from Hunter school and go exclusively by their Hunter names. Interestingly, Mirage and Eclipse, having known each other for as long as they have, still call each other by their old names.
People of Hair Color: All the witches have red hair. Someone with red hair who is not a witch or a Cousin is considered very unusual.
Power of the Void: Mirei discovers that the Void does have magic, which can only be accessed by witches who have recombined with their Doppelgangers. This makes her extra special since she's the only one in the story who can use it.
Redheaded Hero: All the main protagonists except Eclipse. It comes with the in-story demographic.
Redheaded Stepchild: Mirage was ostracized and bullied at Silverfire because of her red hair. Later, so was Indera, while Amas dyes her hair to avoid this.
Red Oni, Blue Oni: Arguably, Mirage and Eclipse, or even Mirage and Miryo (because everyone's blue compared to Mirage). Later, and less ambiguously, Mirei is red to Satomi's blue.
Split At Birth: Miryo and Mirage, and every other witch child and her doppelganger.
Take Me Instead!: Mirei tries to do this to keep Eclipse's falsely sworn oath from killing him. In a miracle of Divine Intervention, this ends up saving them both.
Well-Intentioned Extremist: the Primes in the first book, Shimi and Arinei in the second.