Nemuri Kayama, also known as the R-Rated Hero: Midnight, is a Pro Hero and faculty member at U.A. High School, who teaches Modern Hero Art History. Nemuri is a tall, curvaceous woman with sky blue eyes, which tilt downwards in the center; framed by a set of rather long eyelashes. She has abundant spiky dark purple hair which is made up of layers of varying lengths, the longest ones reaching down below her waist. Her chin-length bangs that are 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 has a small beauty mark below her left eye, as well as red-painted nails. Her hero costume is very similar to one of a traditional dominatrix. She wears a breastless, black leather leotard—similar in style to a corset—over a thin, skin-tight white bodysuit (flesh-colored in the manga), which accentuates her voluptuous figure. The center strip of her leotard is embellished with red gemstone-like accessories in a vertical pattern, extending from her collar to her midriff. She also wears translucent, black, thigh-high garter stockings, which are attached to a burgundy utility belt decorated with gold studs around her hips, a matching pentagonal buckle in its center, and black knee-boots. She has a small red mask outlining her eyes, and a handcuff on each wrist. She is often seen carrying a flogger-style whip. The white bodysuit is made of thin material that is easily rippable so she can more easily use her Quirk. Nemuri has stated in an interview that she is trying different materials to find out what works while adhering to costume regulations. During her years at U.A. High School, Nemuri's original costume was much more revealing. Her breasts were censored by a black protective plate, and wore a dog collar. She wore only undergarments, which were covered with a utility belt that held her whip. She was otherwise completely bare aside for an unbuttoned, high-collared trench coat. She also had large angular shades, different from the mask she wears now. Nemuri is a very playful and flirtatious person with an unpredictably serious and temperamental side to her. She gets angry whenever someone interrupts her or when they insult her, and, when it comes to insults, she is especially sensitive about her age. Nemuri has no shame for dressing or acting sexually in front of young students and appears to act on whims most of the time. When she accepted Mashirao Ojiro and Nirengeki Shoda’s request to resign from the tournament, she commented that their naivety "turned her on". She was also very excited to see the chivalry displayed by Eijiro Kirishima during the tournament when he shook Tetsutetsu Tetsutetsu’s hand. Her love of "youth" is also a reason she gets angry when someone mentions her age or calls her old. When Class 1-A needed to decide on code names for their internship, Nemuri displayed her willingness to help her students by making sure they chose names that would represent themselves well. During the Final Exams, Nemuri admitted to Minoru Mineta that she has a sadistic side and enjoys dominating others. She can be impressed with those who resort to genius plans, as she was amazed by Minoru using tactical thinking to defeat her by leaving her in place before passing the gate. Despite her flirtatious personality, Nemuri is intelligent, perceptive, and articulate. For instance, in an intervew, she logically explained the reasoning behind some heroes having revealing costumes to make full use of their quirks, thus leading to "sexy" costumes, and how her previous "scandalous" costumes single-handedly led to the institution of hero costume regulations. However, in reponse, Mt. Lady commented that Nemuri simply likes dressing the way she does for attention.