A Super Attack can be automatically triggered once the attacking character's Ki Meter is full. Each character's Ki Meter needs 12 Ki to be filled up completely. Collecting Ki Spheres with the same color of the attacking character will allow him/her to collect twice the amount. A perfect chain of same-colored spheres will give you 12 ki spheres. Super Attacks are very powerful but you still need to take into consideration the type of the character Attacking and Defending.
You can also increase the level of a character's Super Attack in Training.