I finished tagging the remaining D4DJ characters and added all of the Assault Lily girls. My best guess for the others in the back with Muni are perhaps Himari and Riri, but it's such little/unclear detail back there I'm not going to bother tagging them.
Regarding the fight in the background, Michelle is from Bandori and Tokyo Tower is a prominent symbol in Revue Starlight, but I'm not familiar with D4DJ or Assault Lily so I don't know what the other things are, aside from the daruma doll. If anyone knows what the metagross-looking thing is or the other thing holding the axes, I'd be happy to hear about it.
The metagross-looking thing next to Tokyo Tower is a Huge, one of the monsters they fight in Assault Lily. (Specifically, it's the one from episode 1 of Assault Lily Bouquet.)
It doesn't imply that since this is just how volume 1 played out, minus all the blood.
It's likely based on the season 2 episode where Aqua imagines this specific scenario in order to properly guide his acting through emotions rather than calculted gestures or imitation of other performances.