Innate Attack: Ki Blasts/Kamehameha

A friend that I am playing a Dungeon Fantasy campaign with asked for something similar for his Martial Artist character. This is probably a straightforward attack. He really likes Dragon Ball Z but I've never watched it. The key elements for describing the attack seem to be:

1. It's a launched projectile
2. It's got a moderate ability to modify the power level
3. It specifically calls out the need to use both hands
4. It has knockback
5. It depends on a longer charging time

So let's see how to stat this out.