Nemuri was a tall, curvaceous woman with sky blue eyes that tilted downward in the center and were framed by a set of rather long eyelashes. She had long, thick, spiky, dark purple hair, which was made up of layers of varying lengths, the longest ones reaching down below her waist. Her chin-length bangs were split into three sections: two swept to the sides and one over her face, going diagonally down to the left between her eyes. She also had a small beauty mark below her left eye, as well as red-painted nails.

Her hero costume was remarkably similar to one of a traditional dominatrix. She wore a breastless, black leather leotard—similar in style to a corset—over a thin, skin-tight, white bodysuit (flesh-colored in the manga), which accentuated her voluptuous figure. The center strip of her leotard was embellished with red gemstone-like accessories in a vertical pattern, extending from her collar to her midriff. She also wore translucent, black, thigh-high garter stockings, which were attached to a burgundy Somnambulist allowed the user to put targets to sleep by exuding a sleep-inducing aroma from their skin.

Somnambulist was described as being more effective on males than on females, giving Nemuri an obvious advantage against men.[1] Regardless of that, anyone who breathed in enough of the aroma would eventually fall into a deep slumber, which would make it difficult for opponents to confront Nemuri at close range.

In the anime, the mist that represents the Quirk's aroma is colored violet. Weaknesses

It is possible to avoid the effects of Somnambulist simply by not breathing in the aroma. This put Nemuri at a disadvantage against opponents who had their mouths covered by masks that could function as air filters. Alternatively, an opponent could cover their mouth with something to hold their breath, as demonstrated when Minoru Mineta avoided the Quirk's effects by covering his mouth with Hanta Sero's Tape.

Somnambulist's sleeping aroma was also less effective against women.