In the narrative of Sailor Moon R, Emerald is a significant antagonist and a high-ranking member of the Black Moon Clan, a group from the future that seeks to conquer Crystal Tokyo. She is also known by her original Japanese name, Esmeraude. Emerald is a tall, vain, and strikingly beautiful woman who cultivates a goddess-like image. She has long, flowing green hair, red eyes, and a distinctive rotated crescent moon mark on her forehead. Her attire typically consists of a fitted black dress adorned with three large emeralds, paired with dark green opera-length gloves and black stiletto boots. She often carries a large, sharp-edged fan, which she may use as a weapon in combat.

Emerald is defined by her overwhelming vanity, greed, and jealousy. She possesses a famously loud and obnoxious laugh and has a self-indulgent personality, as she is easily distracted by luxuries such as fancy cakes and hot baths. Her primary motivation is her obsessive and unrequited love for Prince Diamond, the leader of the Black Moon Clan. She desperately wishes to be his queen and is consumed by a fierce, single-minded jealousy towards Sailor Moon, upon whom Prince Diamond has fixated his attention.

Emerald's role in the story begins when she succeeds Rubeus as the primary field commander for the Black Moon Clan after his defeat. She shows no loyalty to her predecessor, gleefully abandoning him to die in an exploding spaceship and lying to Prince Diamond about the circumstances of his death. Eager to prove herself, she devises a plan to use devices called Dark Wedges, created by Prince Diamond's brother Saphir, to saturate vulnerable points in Tokyo with dark energy, intending to open a gate for the Clan's invasion. She personally oversees these attacks in the present day, sending a series of droids to battle the Sailor Guardians and capture the young Chibiusa. Her jealousy is so potent that she even secretly sabotages Prince Diamond's own efforts, attacking him from the shadows to allow Sailor Moon to escape, hoping to remove the object of his affection.

Her key relationships are driven by her obsession and ambition. Her dynamic with Prince Diamond is one of desperate, unrequited adoration, which he largely ignores. She treats Rubeus with contempt and coldly discards him when he is no longer useful. She holds a deep-seated hatred for Sailor Moon, viewing her solely as a romantic rival. She also interacts with Wiseman, the sinister advisor to the Clan, whom she eventually turns to for power when her own schemes fail.

Emerald's development arc culminates in a tragic and monstrous transformation. Frustrated by her failures and consumed by her desire for Diamond, she goes to Wiseman and accepts a magical tiara empowered by the malevolent Dark Crystal. Despite suspecting a hidden price, her greed overwhelms her caution. The crown initially transforms her into a regal "Queen Esmeraude," but the dark power proves too great for her to control. She is subsequently corrupted and physically warped into a mindless, gigantic black dragon. In this bestial form, she attacks Crystal Palace directly, using powerful physical strikes and breathing fire. It is noted that the dragon is a manifestation of her own corrupted subconscious mind. The Sailor Guardians struggle to harm her until Tuxedo Mask throws a rose that strikes the crown on her head, momentarily stunning her. This allows Sailor Moon to destroy the dragon with the Moon Scepter Elimination. Emerald briefly reappears in her human form, surrounded by a ghostly light, before a dark void opens beneath her and she falls to her apparent death, whispering Prince Diamond's name as she vanishes.