Atomic Fire

From Mega Man - Wiki on Neoseeker

The Atomic Fire attack is a weapon gained after defeating the boss Heat Man in Mega Man 2. It is the first weapon in the series with the ability to charge. It fires a small fireball when the fire button is tapped, a larger fireball when the fire button is held, and a much larger fireball if the weapon is charged for a while. Mega Man's suit is red and yellow when Atomic Fire is equipped.