The camera was always behind them, there are set cameras all over the place...what isn't always in place if cameramen . They move around and try to capture different angles for moments. The actress is aware of how these things work and she uses that to her advantage like with Aqua, but Aqua doesn't have any experience in this field and so he only just learned about how the cameras are all around.
I was so glad that you all realized about how Ai built up her idol career by telling lies to herself and her fans, while Ruby believes the idol industry is the embodiment of love and wants to represent that to the fullest. Aqua knows the dark side of the idol industry and wants to protect his sister not only from the fate of Ai, but also from the darkness of the industry itself. Interesting that he knows they are both reincarnations, but he still has bonded so strongly to Ruby as his sister that he must protect her as a real brother would.