As a human, Mitty was an upbeat and positive young girl. She was almost always smiling and aspired to be "a future White Whistle". Her hair was reddish in color, long, and messy, sticking out at random angles. Some of it seemed to be tied up into a messy ponytail on the back of her head. She wore a tied top and skirt. She also appeared to be slightly more buxom than the children her age.

After bearing the Curse of the 6th layer, Mitty's body became something of an amorphous blob. She became covered in light pinkish fur. On the ends of what is left of her arms were long, sharp claws. She has two cat-like ears protruding at odds angles from her head. Her mouth split upwards and is left hanging open at all times. She is missing her left eye.

Source: Made in Abyss Manga: Made in Abyss Chapter 13, 23, and 45