After the events of the Android/Cell saga and the defeat of Cell and 16's death from Cell, and the death of goku from his sacerfice to not let earth get dystroyed from cell, gohan is the only strongest fighter on earth, the red ribbon army hired you to make the a powerful android to defeat gohan, you worked on it for about 8 months and finish making Android 21 you pressed the button on the remote and she turned on

Android 21 : She open her eyes and looks at you