In R-type II you can charge a shot just like you can in R-Type, however if you charge it long enough, there will be a small window of time when the power bar flashes between orange and blue, release during this time and you will unleash a more powerful charge shot that covers a much wider area.

On the first stage of R-Type II, you will come to an opening after fighting 3 waves of red enemies and a wave of orange enemies. Through the small opening a wave of exactly 10 orange enemies will come flying at you, it might take a few tries but you want to charge up this powerful shot to coincide with most of the enemies being inside of the opening.

Too early and it will miss the last ones, too late and you will either die, or the shot will miss the first two enemies.