Once your mind is totally asleep, the ‘spirit’ get to work into remodeling her new body to her convenance. Said body slowly transform into a young Chinese girl around the same age you were, so probably 11, with long black hairs. The last change is your eyes, that become jade-green.
Or at least, that was the last change before your former body start to loose its humanity. Because once the eyes turn the color of jade, their iris grow to take almost all the visible part while your pupils become cat-like. Your fingers become sharp talons while most of your toes fuse together, becoming four more talons, two by foot, that give the illusion you have cloven hooves instead of feet. Two horns of a very impressive size and just as sharp than your talons grow from the sides of your forehead. Then, two holes appear in the qipao, one small just above your ass were you grow a long, strong and very flexible tail tipped by a dagger-like blade, and a keyhole on your back to let two enormous bat-like wings to pass.
As soon as the demoness finished ‘renovating’ your body, she force your mind to wake-up while making sure she still had a tight grip on the controls, so to speak.
Once you were fully awake, she made a show to use her powers to make a full body mirror so she could admire her handiwork. (Which forced you to do the same, to your growing horror.) Without warning, she bowed to her reflection and said "Hello human! I'm Princess Ling, heir to the Nüying clan of succubi. I used to live in China, long ago. But some day an exorcist sealed me in my favorite qipao after I turned his daughter into my latest subject."
"For now I still need to wear this old thing to stay in this body, but don't worry your stupid little human mind, once I stayed in it for a whole week without damaging it I'll be there to stay. The only drawback is that, since it's the body of a kid, I have to wait for it to naturally grow to adult-hood before I can do my job again…"
Then, Ling used her demonic powers to go back to her human appearance, the one she had before her demonic aspects manifested themselves in your former body.