The evil 21 leaves, along with her good counterpart, 18, and 17 resolving to cease her in reminiscence of their fallen good friend, Android sixteen. As the game progresses, 17 notices something unusual about the new android, who was continuously groaning and screaming, at one level 17 even saying he disliked her tone. However, when discovering Krillin, who was trying to rescue 18, 21 finally snapped and told about “eating” him which shocked 17. Luckily, the group managed to subdue Krillin and 21, with 17 having to maneuver Krillin’s body somewhere. After this incident, 17 and 18 demand an explanation from sixteen and return to 21’s lab, the place it is revealed by sixteen that Android 21 was a human transformed into a Bio-Android from the cells of various fighters and scientists.
16 states they planned to use the soul link system developed by Dr. Gero to suppress the evil 21. Android 21 recreated 16 because of him being designed after her human son and would have lived peacefully with him had it not been for her cravings and rising evil persona. Goku’s final wish of Shenron after the battle with Syn Shenron restored the lives of those who did not should die between the Super 17 and the Shadow Dragon Sagas, together with Android 17.
Pan’s ploy to have Gero bring 17 to a halt is ruined when Dr. Myuu reveals his programming positioned him in full control of the super android, and so Super 17 kills Dr. Gero, for the second time. Piccolo and Dende create a gateway between Hell and Earth, permitting Goku to escape and confront Super 17, before another Z Fighters can be killed.
However some of the cells (implied to be these of Kid Buu as his clones share the unique’s character) went uncontrolled causing Android 21 to develop cravings to turn individuals into food to eat and take in their energy like Cell and Majin Buu. This triggered 21 to develop an evil split personality which is vying for management of Android 21’s physique.
As a result, 17, 18, and Good 21 join forces with the Z Fighters to combat 21 and the clones which she begins feeding on to fulfill her growing hunger. The Good 21 ultimately sacrifices herself to ensure her evil counterpart both are destroyed by Goku’s Spirit Bomb, to prevent herself from being finally being overcome by her cravings and turning on her newfound pals as she had with 16. When Goku tells his associates not to worry they’re afraid he plans to revive 21 with the Dragon Balls however he notes that may fly in the face of 21’s sacrifice and that he instead plans to ask King Yemma reincarnate 21’s soul like he had carried out previously with Kid Buu’s. Wanting to guard her fellow Androids, 21 transforms right into a blue-eyed model of her true type with the help the soul hyperlink.
She manages to defeat Cell, but her cravings and evil persona take control and she or he destroys 16 when he tries to cease her from eating Cell. They manage to help 21 come to her senses and overwhelmed with grief over having killed 16, Android 21 splits into Android 21 (Good) and Android 21 (Evil). The evil 21 inherits most of 21’s power and eagerly consumes Cell inflicting her pores and skin to alter colour and acquire patches on her pores and skin similar to Cell’s spots.