Android 21 is described as a tall, curvaceous scientist with a very slender build, blue eyes and long bushy auburn hair. She wears glasses, has a gold ring on her left middle finger, and black nails. She wears a pair of hoop earrings, a sleeveless, short blue and red checker pattern high neck minidress with opaque black tights, matching black detached arm sleeves, and blue (left foot) and red (right foot) ankle heel boots with gold tips. She also usually wears a white lab coat (with the Red Ribbon logo on the left shoulder) with her outfit.

In her true form, Android 21 keeps her curvy body, her skin turns pink, her hair becomes white with a pink tint, her ears become pointed, her eyes changing depending on if her evil half takes over, and she gains a long prehensile tail. Her attire changes to a black tube top, keeping the black arm sleeves with gold bracelets at the ends, her boots become black, and also gaining white baggy pants. It's noted that she most resembles a Majin in this form. Her eyes slightly vary depending on which moral alignment she represents. In her good representation, she retains the eyes from her human form. In her evil representation, her eyes instead are more similar overall to that of a Majin.

Kind and motherly: She acts like a gentle, concerned woman—e.g., she agrees to help Android 18 and shows genuine worry for others. She develops a deep, protective, adoptive mother-son bond with Android 16 (modeled after her human template's son, Gevo), repairing him and treating him with affection even without full memories of her past life as a human (possibly named Vomi, Dr. Gero's wife). She mourns his death deeply and honors his memory.

Gentle and reluctant warrior: Like Android 16, she dislikes fighting in general and is a peaceful soul at heart. She only fights to protect innocents, friends, or loved ones. She's somewhat dorky and timid socially—gets embarrassed easily (e.g., by Goku wanting to spar), has awkward moments (like overeating string cheese or bantering with Gotenks), and even apologizes mid-fight after the split.

Self-aware and self-sacrificing: She feels guilt over her hunger's effects, views herself critically (heroic self-deprecation), and is determined to atone. After splitting, she works with the Z Fighters, links with a human soul (from Android 18) to better control herself, and ultimately sacrifices herself to stop her evil half—fearing she might eventually lose control and hurt her new allies (a trait mirroring Android 16). She's aware she's "technically not even ten years old" despite her adult appearance and regrets missing out on a normal life/adolescence.

Shared interests and bonds: She loves sweets (especially macarons, like Majin Buu) but resists turning people into them. She's friendly with Good Buu due to their shared biology and sweet tooth. She bonds with Androids 17 and 18 over their shared "Android" struggles and respects Dr. Gero's brilliance as a scientist

Being created from the cells of countless warriors and scientists, Android 21 is one of the most powerful Androids in the series and the most powerful female Android created through Dr. Gero's research. Like Majin Buu and Cell, she can increase her power by absorbing other life forms, which she does by turning them into sweets and eating them increasing her power.

Flight - The ability to fly using ki.

Ki Blast - The most basic form of energy attack.

High-Heeled Ki Slash - Used in Xenoverse 2 as part of the Ultra Pack 2 DLC.

Tail Attack - In her true form, Android 21 can attack enemies with her tail as part of certain combos. She can also thrust her tail into the ground, then have it erupt from the ground to deliver a surprise attack, taking advantage of her ability to extend her tail which can presumably be attributed to either her Frieza Race, Namekian, and Majin cells or a combination of all three.

Hungry Beam - A move Android 21 uses to turn people into food.

Sweet Tooth - One of Android 21's Meteor Attack (Level 3 Super) in FighterZ, which is said to work like Majin Buu's though is fired as a finger beam. Android 21 turns the opponent into a dessert (such as a donut, macaroon, or cupcake) and then taste tests it by take a bite out of the transformed opponent, regaining some health. If this attack finishes the enemy off, she eats the opponent completely in FighterZ.

Absorption - In all scenarios, she absorbs many clones. In the Super Warrior Arc she absorbs Nappa, Cell, the Ginyu Force and finally Frieza. Like Cell and Majin Buu, this makes her more powerful. Android 21's absorption resembles a combination of Majin Buu's Candy Beam and Cell's absorption ability as she can increase her power by turning others into food and eating them.

Connoisseur Cut - A move that lets Android 21 absorb an opponent's energy and use up to four of her opponents moves. There is a pool of eight moves she can copy with their availability depending on the enemy she took ki from. Notably, ki attacks copied with this move are red and black in color.

Savory Slicer - One of Android 21's Super Skills in Xenoverse 2 as part of the Ultra Pack 2 DLC.

Appetizing Rush - One of Android 21's Ultimate Skills in Xenoverse 2 from Ultra Pack 2 DLC.

Solar Flare - One of the moves Android 21 can use after using Connoisseur Cut. It is functionally identical to Krillin's version but can be used in the air. Obtained from enemies somewhat connected to Goku.

Kamehameha - One of the moves Android 21 can use after using Connoisseur Cut. Obtained from enemies somewhat connected to Goku.

Majin Kamehameha - Due to possessing Majin Buu's cells, Android 21 can utilize this pink imitation of the Kamehameha used by members of the Majin Demon Clan. One of Super Skills used by Android 21 (ironically in her normal human form instead of her Majin-like Transformed state) in Xenoverse 2 as part of the Ultra Pack 2 DLC.

Homing Energy Blast - One of the moves Android 21 can use after using Connoisseur Cut. It is similar to Piccolo's version, but she can only conjure a single orb at a time. Obtained from alien or godly enemies.

Continuous Energy Bullet - One of the moves Android 21 can use after using Connoisseur Cut. A series of rapid-fire blasts. Obtained from enemies connected to Vegeta.

Sticky Energy Blast - One of the moves Android 21 can use after using Connoisseur Cut. It is a command grab where she throws the opponent across the arena. Obtained from enemies connected to Vegeta.

Barrier Sphere - One of the moves Android 21 can use after using Connoisseur Cut. Obtained from enemies connected to androids.

Explosive Energy Blast - One of the moves Android 21 can use after using Connoisseur Cut. it is a pair of energy blast fired at the ground. Obtained from enemies connected to the Androids.

Instant Transmission - One of the moves Android 21 can use after using Connoisseur Cut. Also used to teleport Android 21 to the Sacred World of the Kai. Obtained from alien or godly enemies. In the Super Warriors Arc, Android 21 learns it via mimicry after seeing it being used by Goku to travel to the Sacred World of the Kais.

Hors d'Oeuvre Stab - Android 21 flies down towards the opponent from the air and strikes them into the ground.

Total Detonation Ball - Android 21 launches a ball of ki that flies across the screen and explodes on impact. The heavy version of this move will discard all her acquired moves in exchange for extra power.

Total Evasion - Android 21's Evasive Skill in Xenoverse 2 as part of the Ultra Pack 2 DLC.

Absolute Release Ball - A bigger version of Total Detonation Ball, used by Android 21 to destroy Android 16. It is normal Android 21's super attack in Dragon Ball Heroes. In Dokkan Battle, it is used by Android 21 in her human form as her Super Attack, though with her good personality in control of her body.

Photon Swipe - A move where Android 21 produces a Death Beam-like Photon Wave that explodes where it hits along the ground.

Excellent Full Course - Android 21's other Level 3 Super, where she flies into the opponent, hitting them with a flurry of dash attacks, before striking them to the ground and fires a ki blast from on top of them.

Survivability - Thanks to possessing cells from Frieza, Cell, and Kid Buu, Android 21 possess great survivability and endurance.

Regeneration - Thanks to possessing cells from Piccolo, Cell, Kid Buu and Good Buu, Android 21 possess one of the greatest regenerative capabilities in the series.

Fission - After destroying Android 16 in the Android 21 Arc, Android 21 releases her evil hunger persona as a separate entity. This ability was apparently inherited from her Majin cells instead of her Namekian Cells, as the good and evil halves are not life linked as revealed the good half reveals during a special conversation with Piccolo and Tien.