*Android 21 (Evil) (人じん造ぞう人にん間げん２１号ごう（悪あく）, Jinzōningen Nijūichi-Gō (Aku)) is the true main antagonist of Dragon Ball FighterZ.

While her good half and 21 were one, Android 21 (Evil) appeared as a black specter, in the silhouette of Android 21. She also appeared with a pink and blue aura.

In her true form, she looks exactly the same as Android 21 (Good), except she has red eyes and black sclera, as well as having a slight pink color to her hair, as opposed to the good one's pure white hair color.

Upon eating and absorbing Cell she undergoes a transformation, where her skin turns gray and she has dark purple spots throughout her body like that of Cell's. She also gains a purple tint to her hair.

As noted, this side of Android 21 is pure evil, having nothing but a desire to devour all the Z Warriors to satisfy her needs of eating and gaining more power to the point of being seen as nearly insane. However, these desires do not cloud her thinking as she is capable of making rational decisions and assess the situation at hand. Sadistic and sociopathic, 21 will go to extreme lengths to gain the power she desires.

Fitting with her evil nature, Android 21 was disgusted with her good self's way of thinking and views who had no will or desire to consume others for their power (similar to Frieza who is disgusted by Goku's good heart). However, she found this to be pleasing since it left her with the belief that no one could stand in her way and stop her from eating everything she wanted, mirroring Good Buu and Evil Buu's dynamic. Her personality resembles Android 21's from the previous arcs as she was essentially under her evil persona's complete control in those arcs.

Upon meeting Goku, Evil Android 21 gushed in his presence while referring to him as her "sweetie Goku" and proclaimed her intentions to eat him, licking her lips at the thought of consuming him. However, she reconsidered confronting him as she decided to save the best for last presumably due to the influence of Cell's cells, but she still took the opportunity to "snag" Instant Transmission which she used to escape. Ultimately, though, she eventually started losing control as she began running out of clones with her impulsiveness and need to feed her hunger increasing.

She also believes that her good self is a hypocrite due to her refusal to not consume others as her hunger will only continue to grow worse and even encourages her to give in to her hunger believing it is the only way her good self can hope to stand a chance against her; this is presumably to make her good self a more enticing meal, though it may also be influenced by her wanting a decent challenge due to the influence of her Saiyan cells as she believes only her counterpart could match her. She is also caught off-guard by her good self's willingness to sacrifice her own life to stop her.

Before the fission, while her evil personality was in control, she expressed a belief that Androids like herself, Android 18, and Android 17 had no need for human families when she attempted to eat Krillin. This belief likely explains why she had no love for Android 16 whom Android 21 murders in all three arcs while her evil side is in control, though in the Android 21 Arc this results in her fission due to her "heart" regaining control because of the anguish and guilt over his death—especially since this could have subconsciously reminded of her human son Gevo's death as 16 was built in Gevo's image. She also does not dismiss the possibility of seeking galactic conquest, which was implied to be her original purpose, although it is unclear if she was programmed to seek it and/or if it was due to the influence of Frieza and King Cold's cells. In addition, despite her evil nature and use of his technology, she had no real affection for Dr. Gero and only utilized his technology to suit her own goals which were all centered around satisfying her urge to feed and grow stronger, with galactic conquest a secondary objective at best.*