Reportedly the outfits for ML 12th will differ by day (maybe the stage will too).
Day 1 with Reika was vaguely described as spacesuit-like and having the imagery of jellyfish (see-through parts?). Reika's image is of the sky so I guess that makes sense.
Day 2 with Kaori was described as being uniform-like since she was a teacher I guess. I think Sound of Music was brought up before regarding the theme. Maybe there will be musicals!