Wings of Bluestar

From what I could find online (as this was my second to last achievement), a hidden risk star has a (very low) chance of appearing whenever an enemy bullet is destroyed.

I took Aya, the female pilot, through the first level, upgraded her so she had her shield power up (A blue/red spikey ball in front of her ship) and got to the boss of the stage. From there, I let him fire on me absorbing the shots with my shield as I shot at him.
As my shield went down, so did his health, turning all of his bullets into blue gems with one red star in the middle.

I'm unsure which caused the star to appear, his bullets becoming gems or his bullets being destroyed by my shield, but I still got this achievement the first time I actively tried to go for it.
I would welcome any and all input so I can make this solution more concrete, however.

Happy hunting (>*_*)>