Rainbow are indeed on Makestar, but like with Nine Muses, their project is a photobook.
https://www.youtube.com/watch?v=CHbx2QBGGr0
As I’m writing this, they’re already over halfway to their goal, and all the autographed copies are sold out.
No point to this article except to make you aware of glorious Rainbow and their glorious visuals will be in a photobook.