This is so clever, I'm amazed I've never seen it before and only slightly envious I didn't think of it myself.
It was a little unclear at first; I had no clue that I was supposed to be picking up the other rectangles and had assumed they were obstacles or enemies to be destroyed, but once I figured that out, it clicked in a really fun way.
But oh man it's hard. It's incredibly easy to get overwhelmed, and I found that the further right on the screen I got, the less hope I had of recovery, and it's remarkable easy to lose party members with how spread out they are and how many bullets are on screen at once.
That said, I hope you iterate on this. Because I would probably play a lot of it.