They should make GTA DBZ. You play as an android who can't be sensed by the Z fighters and drive around doing missions for Gero. If you do too much the Z fighters start to catch on, rather than only the police. Which Z fighter appears first is quite random, but some zones attract certain Z fighters more. For example West City is a hotspot for Trunks, Vegeta and Yamcha and to some extent Krillin. Satan City becomes a hotspot for Gohan (or sometimes Great Saiyaman) partway through the game, anywhere near Roshi's or Mt Paozu is a hotspot for Goku and Gohan. If you cause damage that makes a high-pitched noise, Piccolo is more likely to appear afterwards. You can fight the Z fighters or you can run away and hide - you can sense them but they can only rely on their sight, intuition or environmental cues.