I wanted to give Akatsuki a good Magical girl outfit, and fortunately Miyu's normal colorations make for a very good fit for her. Unfortunately, there really isn't an official "Tempest" version for Miyu, but I've seen a lot of fan versions out there that use this coloration, so I decided to use these colors.
Also, Akatsuki has a very good imagination, so that's why she can fly!