When you complete the following tasks the corresponding character will become unlocked.
Complete the Android 21 arc in Story Mode.
Complete 'Hyperbolic Time Chamber Course (Hard)' in Arcade Mode with an A rank or higher, or earn 500,000 Zeni.
Complete 'Extreme Gravity Spaceship Course (Hard)' in Arcade Mode with an A rank or higher, or earn 300,000 Zeni.
Unlock Secret Characters in Story Mode:
When you reach Level 40 in Story mode two additional characters that are not officially part of the story can be unlocked. These characters can be used in any of the Story mode campaigns.
Reach Level 40 with Goku (Super Saiyan).
Reach Lv. 40 with Vegeta (Super Saiyan).