To be honest, on the top of my mind:
-I'd love some discreet star/spatial accents in between the seams of the gun, nothing too drastic but enough to feel like the gun is held together by some strange cosmic power.
The gun would have some gold and iridescent white in terms of colour, the gold acting as a complementary colour to the dark blue of the spatial effects and the iridescent white giving the idea of some alien weapon.
-Pew pew effects akin to a shooting star but with good impact, which could be difficult to implement. Maybe it could be something like a small star exploding inside the gun and pushing the bullet out of the chamber, which would lead to a sharp shooting sound preceded by a big fiery BANG ?
-Constellations/dark matter forming the visor in ADS ?
-Reloading by disintegrating/reforming the magazine/bullets into existence?
Or maybe the magazine could be something where we load stars in instead of changing the ma...