Queen Metalia is a malignant, amorphous energy being who serves as the true mastermind and leader of the Dark Kingdom in the Sailor Moon anime. She is the one who granted Queen Beryl her power, and she operates as the hidden force behind the Dark Kingdom's efforts throughout the first story arc. In the English-language version of the anime, she is referred to as the Negaforce. Rather than possessing a fixed physical form, she appears as a shadowy, formless mass of dark energy, often depicted as an enormous presence that can expand to engulf entire areas and spread chaos and violence among people.

Her background is rooted in the ancient conflict between the Moon Kingdom and the Earth. During the era known as the Silver Millennium, Queen Metalia exploited the resentment and negative feelings of certain humans, including a woman named Beryl, whose affections for Prince Endymion were manipulated for Metalia's purposes. This manipulation helped trigger a war that led to the fall of the Moon Kingdom. Following that conflict, Metalia was sealed away, with Queen Serenity using the power of the Silver Crystal to contain her. In the modern era of the anime, she manages to influence events once again, bringing a reborn Beryl into her service and commanding her to find the Silver Crystal so that it can be used to free her.

In terms of personality, Queen Metalia is cunning, cruel, and sadistic, and she takes pleasure in inflicting pain and despair on her enemies. As an embodiment of darkness, she deliberately corrupts others, taking advantage of their most hopeless situations to turn them toward evil. She is not motivated by revenge, love, or personal ambition in a human sense; instead, she is an impersonal and existential force of darkness that seeks to absorb all energy, destroy light, and remake the world into a realm of darkness and chaos.

Her role in the story is that of the supreme antagonist of the Dark Kingdom arc. She is the ultimate source of the Dark Kingdom's power and the one who directs its campaign to gather energy and locate the Silver Crystal. Although Queen Beryl is the visible leader of the Dark Kingdom, Metalia is the true power behind her. In the final confrontation, she becomes powerful enough to resurrect on her own and takes possession of the dying Beryl, transforming into a towering, goddess-like creature. She also takes control of the reincarnated Prince Endymion, using his body as a host and forcing Sailor Moon to face him in battle.

Her key relationships are defined by her role as a corrupting and commanding presence. Queen Beryl is her primary servant, having been given power by Metalia and manipulated through her desires. Prince Endymion becomes another important figure, as Metalia uses him as a host to further her aims. Sailor Moon is her direct opposite, representing love, compassion, and hope, while Metalia embodies emptiness, malice, and despair. The final battle hinges on this opposition, as Sailor Moon must ultimately use the full power of the Silver Crystal to purify and destroy Metalia, restoring peace and reviving the fallen guardians.

Her notable abilities include absorbing energy from human hearts and from the environment to increase her size and power, expanding her dark form to cover vast areas and spread chaos among people, manipulating and corrupting others through their negative emotions, and possessing individuals to use them as hosts. She can generate destructive energy and is essentially immune to ordinary forms of attack, since she is a being of pure dark energy rather than a physical creature. Her only true vulnerability is the full power of the Silver Crystal, which is what ultimately brings about her destruction. In the anime, her development follows a path from a distant, sealed malevolent force to an awakened and fully manifested threat whose defeat marks the end of the Dark Kingdom arc.