What is Radiant Star?
Radiant Star is a bow weapon. It would work similar to bomb by being charge attack only ranged weapon. I got this idea from the behavior of old shard bombs. What would be a "gun" which would be charged for a long range "missile"? That must be bow. For ammunition, it would use pieces of different type of

What does it look like?
Concept
It's actually Wrench Wand. Punch didn't like being Mender back then so he punched his old Wrench Wand. Suddenly, it looked like a bow. All he did was stringing that wrong shape wand to a bow (...and that's how Punch started Punching with his hammah).
To be honest, this idea for the look was completely random. I just thought about shard first. Then I got the vision of Wrench wand. No, that's not bow, but it does have shard. if you reshaped it? O, bow.

How to obtain this weapon?
Craft it with a recipe (purchase from Hall of Heroes),
Or...
If there was a side quest/mission system.
Side Quest: Punch's Story
After completing it, you would get the recipe for this weapon + you could ask Punch to upgrade it for you for required materials and crowns + energy.
Yeah, this stuff goes to other suggestion if anyone is gonna suggest it. I think it could sauce this game a bit more.

Weapon function:
Basicly, it could work like those old shard bombs, just firing single direction shards. Ofcourse, it could get some sort of spread shot at higher ranks but not sure if it would work in terms of balance. The one and only attack, charge attack, would require the same charge time as Biohazard. Only difference would be that once you release charge, it would instantly fire projectile and let you run without stopping.
I think it could be actually interesting to see this, because it could be like reversed reload of gun. You first reload it, then fire it without stopping. There could be this one thing which would make it balanced compared to current alchemers: No shield cancel/weapon switch abuse.

There's not many piercing guns so this could go there. Different variations (Shadow and Elemental) could have just different color shard & projectile

Names for each star rank version?
I have no idea. 2* would probably be Punched Wrench Bow and 5*, in honor of Radiant Sun Shards (and ISB), would be Radiant Star (I did think of Solar Star but it could sound soo much like Polar Star, Cave Story *cough*)

That's all folks
I tried to keep it short and not go blahblahidk.
Atleast I tried. v_v
*snfsnfsnf*
I smell...
SUNSHAAAARDS!

Ps. I'm lazy forumer/stalker.