Emerald Sustrai

"Mercury, I will seriously pay you to shut up."

- Emerald, to Mercury

Emerald Sustrai is an antagonist in the world of RWBY. She is an associate of Cinder Fall and the partner of Mercury Black.

Appearance
Emerald is a slender female with dark tan skin and ruby red eyes. Her hair is a light, mint green cut with a straight fringe and bangs, as well as two long locks on each side, in the back. She wears two bronze-colored rings on her middle fingers as well as a pair of high-heeled shoes.

Originally, her attire consisted of an intricate, exotic-looking white top and olive undershirt, on the back of which is her personal symbol. This symbol is in the shape of a cut gem, most likely referring to her name. This was intended to be accompanied by white shorts, decorated with what appears to be a gold coin-plated belt, with four gold chains draping around her back from two of the coins and what seems to be a green loincloth.

She also wore a gold, three-ring armband on her left arm and a string of gold beads near the same wrist. As of Volume 2, her outfit has changed somewhat. Her top has thinned, her undershirt is now shallow-cut, and her armband and beads no longer seem to be made from gold.

She now also wears white pants and brown chaps that end at her calves and an overlong belt, twice-wrapped, where she keeps her weapons as well as a single pouch. Her hair is also noticeably fuller and longer and her irises are wider.

Background
Emerald lived in Mistral's city before being recruited by Cinder Fall. She lived day to day without a guarantee of enough food, always resorting to stealing to get by. Cinder saw her use her Semblance to steal a ring from a jeweler and asked her to come with her, guaranteeing a source of food. Cinder later recruited Mercury Black, and the three have traveled together since.

The trio first appealed to Adam Taurus of the White Fang, proposing an alliance. However, they were turned down. But, the three were able to ambush and sap Amber of half her Maiden abilities, before retreating due to the timely intervention of Qrow Branwen.

They were able to leverage Adam into their alliance after killing many of the members in his camp. Adam was forced to accept the offer, where the three would provide him with resources, such as Dust and funding, or face death if he refused.

In the post-credits scene for Volume 1, Emerald and Mercury are seen accompanying Cinder to a meeting with Roman Torchwick.

Volume 2
In "Best Day Ever", Emerald appears lost and runs into the shop owner of the newly reopened From Dust Till Dawn, asking for directions to a certain address. As she rounds a corner, Mercury states that he knew she was lost and she offers to pay him to be quiet using money she stole from the shop owner. They arrive at a book store owned by a Faunus named Tukson.

Emerald begins to ask if he has certain books because of his shop's catchphrase, but she eventually asks him for a book he doesn't have. Things turn serious as Emerald reveals that she knows he is planning on running from the White Fang and that he knows why they are there. She asks him if he is planning to fight back and he shouts "Yes" before lunging at her. She ducks under him and Mercury kicks him as he is in the air; killing him.

Emerald and Mercury then return to Roman's base and he questions where they were all day; taking the address from Emerald's pocket without her noticing. Emerald and Mercury confirm that they were cleaning up Roman's mess. When Roman threatens them, Cinder appears and Emerald informs her that they killed Tukson; but Cinder seems more annoyed at their actions as it risks ruining her plan. Emerald then leaves with Cinder, but shows Roman that she managed to steal his lighter.

In "Welcome to Beacon", Emerald is seen with Mercury and Cinder inside Beacon Academy, posing as students from Haven Academy. She bumps into a running Ruby while walking down a hallway. Emerald helps her up, but tells her to mind where she is going. She is then redirected with Mercury and Cinder by Ruby who points them in the direction of their building as transfer students.

In "Extracurricular", Emerald is seen observing a battle between Pyrrha Nikos and Team CRDL, and later Pyrrha against Mercury. Later that day, in a dorm room with Cinder and Mercury, they all begin to talk about Pyrrha's semblance, and how skilled she is, as also listening to Cinder's plan.

In "Dance Dance Infiltration", Emerald and Mercury are seen entering the ballroom together. From here, the duo spends the evening keeping track of the attendees, watching to see if anyone could interfere with Cinder's infiltration of the Cross Continental Transmit Tower. At one point, Emerald warns Cinder that James Ironwood is leaving to check on the tower. However, Cinder is able to finish her task and return to the dance before he can see her. Emerald then lets Cinder take her place as Mercury's dance partner for the remainder of the evening.

In "Breach", Emerald assists Teams RWBY and JNPR in killing Grimm; easily slaying an Ursa using her weapons. She is later present as Adam Taurus appears by Cinder's side, explaining that the White Fang will listen to him, despite numerous losses in the caves.

Volume 3
In "Round One", at the Vytal Festival fairgrounds, Emerald steals Ruby's wallet before returning it to her. She strikes up a friendly conversation with Team RWBY, and it is revealed that she is participating in the tournament alongside Mercury, Cinder and an undercover Neopolitan.

After exchanging pleasantries with Team RWBY, she turns to Mercury and expresses her distaste for all of them, telling him she cannot stand how they always seem so cheery. However, she also shares the intel they had been sent to get: Weiss and Yang will be fighting in round two. Emerald, Mercury and Cinder are then seen spectating the match between Team JNPR and Team BRNZ.

In "It's Brawl in the Family", Emerald is later seen at Cinder's dorm room when Mercury reports Qrow Branwen's presence at Beacon. She asks Cinder if they need to change their plans, but Cinder tells them that they will stay the course. After Cinder gains access to Ironwood's Scroll, she tells Emerald and Mercury to return to their dorms.

In "Lessons Learned", Cinder engineers the next match of the Vytal Festival tournament doubles round: Emerald and Mercury against Coco Adel and Yatsuhashi Daichi of Team CFVY. Emerald and Mercury easily win the match.

In "Fall", after Mercury "loses" his match against Yang and has his leg broken by her apparently unprovoked, Emerald calls out his name and immediately rushes to his side, apparently showing concern for him. This was ultimately revealed to be an illusion created by Emerald, designed to trick Yang into attacking and one of the paramedics into thinking that Mercury's legs are real.

In "Beginning of the End", Cinder, Emerald and Neo evacuate Mercury in an Air Bus to their secret warehouse and head back to the Vytal Festival.

In "Destiny", Ruby sees Emerald in the front row of the Colosseum for the match between Pyrrha and Penny Polendina, even though Ruby was told Mercury's team all went back to Mistral the previous night.

In "PvP", Emerald uses her Semblance to make Pyrrha use her Semblance forcefully on Penny's swords. This causes the wires attached to them to wrap around Penny and split her in half, destroying her. Soon after, Emerald leaves the grandstands of Amity Colosseum.

In "Battle of Beacon", Emerald is seen on a rooftop with Cinder and Mercury, expressing a hint of remorse at the destruction caused by the chaos. Suddenly, she is interrupted by the arrival of the Grimm Dragon, as she remains on the rooftop.

Volume 4
In "The Next Step", after the fall of Beacon, Emerald is seen present at Salem's lair surveying its surroundings and accompanying Cinder alongside Mercury and acting as Cinder's voice due to the loss of her own speaking capabilities.

In "Of Runaways and Stowaways", when a Grimm resembling a small octopus enters Salem's meeting room during Cinder's treatment, Emerald is disgusted and fearful of it. After Salem asks Cinder if she really killed Ozpin, Cinder signals for Emerald to help her respond, but Salem demands she say it with her own words, which makes Emerald step back.

RWBY Chibi
She also appears in the non-canon comedy spinoff series. Here, she works with Cinder and Mercury as an outright but otherwise disinterested villain.

In "Episode 18", she is seen with Cinder, who is plotting in their room at Beacon. Ruby and Nora burst into the room, unknowing that they are evil. Cinder desperately tries to hide a whiteboard with evil plans, but the two heroes are still totally oblivious to it.

In "Episode 19", she makes a brief appearance after being defeated in an evil scheme by Zwei.

In "Episode 20", she tries to hide evil plans and equipment from Neptune and Sun. Later, in a fantasy where world peace is achieved, she, along with the other villains, are extremely distraught.

In "Episode 22", she looks on, embarrassed, as Mercury attempts to get through airport security, but is constantly stopped due to his metal legs.

In "Episode 24", it is revealed that RWBY Chibi was "filmed before a live audience". Emerald and the other villains appear at the end for the curtain call.

Personality
Emerald initially appears to be affable and disarmingly friendly; however, this belies a darker side of her character. On the whole, she seems to be genuinely outgoing and quick-witted, if a little short-fused. She can also act a little childish or petty, such as when she stuck her tongue out at Roman Torchwick after she stole his lighter to mock him.

In "Best Day Ever", when she talks to Tukson about books, she seems to be knowledgeable about books and enjoys reading, as she lists off many titles. She also likes Vale, complimenting the city for its "tall buildings and diverse culture".

She has a tendency to maintain a pretense of friendliness among people in order to gain their trust. This is shown on multiple occasions in "Best Day Ever", where she pretends to be friendly to the Shopkeep in order to catch him off guard and steal his wallet. Later in the same episode, she puts on a friendly act around Tukson before threatening and killing him. Another example is in "Extracurricular"; where she mostly ignores Ruby Rose until she looks directly at her, when Emerald off-handedly smiles and then rolls her eyes when Ruby looks away. In the episode "Round One", she states that she dislikes Team RWBY for their cheery and positive attitude, regardless of her acting as their friend for the time being.

Emerald shows a strong sense of loyalty, specifically to Cinder, whom she appears incredibly eager to please. Accordingly, she is willing to take the initiative to impress her, such as tracking down Tukson and killing him. When Cinder rebukes her for killing Tukson, she defers to Cinder's judgement, quickly apologizing.

Judging from the nonchalant way she talked about killing Tukson, she appears to have no qualms about killing, even lightheartedly joking about it afterwards with Mercury. However, another side of her is seen in "Battle of Beacon", where she seems to be overwhelmed and disheartened at the sheer scale of the destruction and violence taking place, calling it "almost sad".

Fighting
Emerald's weapons can take two main forms - primarily, they act as a pair of dual-wielded pistols, but they can also be converted into a pair of short kusarigama. Emerald seems to be quite adept with her weapons, demonstrating skilled swordsmanship and marksmanship, using both of her weapon forms to fend off Grimm single-handedly in the episode Breach. She later demonstrated the ability to ensnare opponents in her chains and reel them in, even from a great distance.

Emerald is also shown to have impressive reflexes, allowing her to avoid Tukson lunging at her and dodge Coco's rapid gunfire with ease.

Semblance
Emerald's Semblance appears to be Perception Manipulation - the ability to modify the sensory information in a person's head while their brain is processing it. In short she can make one, or multiple individuals simultaneously, see and hear things that aren't necessarily there.

After Yang Xiao Long's victory against Mercury in the singles battle, she made Yang see an illusion of Mercury getting up and attacking her, prompting Yang to counterattack by supposedly breaking his leg. However, in reality Mercury hadn't attacked at all, making Yang's counter seem, to everybody watching, like an unprovoked attack in cold blooded spite. The resulting anger, outcry, shock and distrust from the masses of watchers stirred the Grimm wandering Mountain Glenn, as the Goliaths turned their attention to Vale.

Before this her power had been used to lead Amber into a trap to steal her Maiden powers, where Emerald made Amber see a crying child on the road, prompting the maiden to lower her guard. During her and Mercury's fight against Coco and Yatsuhashi Daichi from Team CFVY, she used her power to hide herself and Mercury from the eyes of her opponents. After Emerald pulled Coco into the canopy section of the arena, Emerald tricked her again by making her see Yatsuhashi come up to her, seemingly victorious, only to have his knock out announced and broadcasted in the other section of the ring. Emerald then seized the opportunity to attack a bewildered Coco and knock her out as well, winning the doubles match.

Her power is however shown to have its limits. Whilst she seems capable of controlling a single mind, controlling any more than that seems to tax her own head severely. After playing an illusion on two medics who came to pick up Mercury, so they wouldn't see his mechanical legs, she was shown to have a considerable headache. It is unknown what the consequences of manipulating any more would do to her mind.

Stealth
Emerald is stated by Mercury to be a master thief, and she has proven that she is adept at pickpocketing, with one victim being Roman Torchwick, stealing his lighter to show him that she was a capable thief after he mocked her. As seen in her fight with Coco, her stealth abilities allow her to move silently and attack from an enemy's blind spot.

Trivia

 * Emerald's appearance greatly resembles that of Cleopatra, who was supposedly cursed by an emerald.
 * In the episode "Best Day Ever", Emerald is established by her actions and Mercury's own words as a "master thief." Later, Roman refers to Emerald as a "street rat," a term used to describe the title character of Aladdin. It could suggest the basis of Emerald's character, as well as her name making allusion to the phrase "diamond in the rough", which is spoken in the Disney adaptation of the tale.
 * Sustrai (capitalized) is the Basque word for "thief" while sustrai (not capitalized) means "roots" or "undercurrent." It may also comes from the Spanish word "sustraer" which means "to steal" or "rob".