DRAGON BALL: Sparking! ZERO

To unlock the branching path make sure you're on the default difficulty setting.

From Gokus saga choose "The Earth's Mightiest Duo" and choose to team up with Piccolo. You will then need to beat Raditz within a certain time limit to unlock the branching path. I believe it is around 2 minutes.

A way to win fast is to charge to 3 bars of ki at the start of the round and use a meteor smash straight away (RT+Y). If it misses or is blocked you can restart the battle and it doesn't take long. Then as he is launched away charge to full sparking mode. In sparking mode get in close (dragon dash with RT+A) and spam X until sparking mode has almost run out, then Y, then immediately use you're Ultimate attack (RT+B).

Basically you want to get into sparking mode as soon as possible and wail on them with X and then use an Ultimate.

You can change to easy difficulty for the rest of the episodes. After completing all the following episodes you will unlock the achievement.