Emerald Sustrai is a character from RWBY. One of Cinder Fall's most trusted subordinates and the partner of Mercury Black, she is an accomplished thief whose semblance allows her to create hallucinations in other people's minds.
Emerald is a young woman with medium-brown skin and dark-red eyes. Her hair is a light, mint-green 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 strappy high-heeled pumps.
Originally, her attire consisted of an intricate white top and an olive-colored crop top, on the back of which is her personal emblem. This emblem 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 crop top 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.
Later, she is also seen wearing the Haven Academy uniform, a more conservative dark gray outfit with a long-sleeved collared top and white armband.
In "Beginning of the End", Emerald was younger, noticeably thinner, and had her hair tied into a ponytail.
Her previous attire was a short olive-colored crop top, and she wore her signature chaps which were torn and belt. Beneath her chaps, she wore dark green pants and plain dark brown flat shoes. She also wore white half-gloves.
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 around 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 demeanor 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 is 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 judgment, 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 afterward 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".