Android 21 can be unlocked by beating story mode or buying the FighterZ Pass. That’s not the only character you can unlock because there’s 2 additional characters you can obtain by playing arcade. Both SSGSS Goku and Vegeta are included if you preordered the game or bought them as DLC for $3, if you did either then you can safely ignore this. For those of you that didn’t, beat both Extreme Gravity Spaceship and Hyperbolic Heavyweight on normal and hard. You unlock hard versions once you beat both courses on normal. You need to get at least an overall A Rank on hard for both courses, otherwise you will not unlock the 2 hidden characters.