Tsuna is able to fire "Hard Sky Flames" from both hands, while "Soft Flames" are released from his Vongola Gear Cambio Forma's arm thrusters, firing twice the amount of power than the X-Burner. Once Tsuna releases this technique, highly powerful flames are released.
The XX-Burner can be fired in two ways. The first method is using the Sky Flame's Harmony characteristic. Using this method, the XX-Burner fires, but doesn't reach its full destructive capability. The second method uses the more destructive attribute of the Sky Flame. Using this method, the XX-Burner causes an extraordinary amount of damage, not only to its intended target, but to the surroundings as well.