Millie is a short imp with red skin and a long devilish tail. She has a pair of thin white-striped black horns and short messy, bob cut-styled charcoal hair with bangs. Her eyes have yellow sclera and long, thick eyelashes protruding from them, with a small beauty mark under the right eye. Her front teeth have a gap as well.

Millie's attire is all-black with a tint of yellow, which consists of a black choker around her neck, a cold-shoulder black crop-top with the straps being held.