Nemuri Kayama (Midnight) - Special winter

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 utility belt decorated with gold studs around her hips, a matching pentagonal buckle in its center, and black knee-boots. She had a small red mask outlining her eyes and a handcuff on each wrist. She was often seen carrying a flogger-style whip. The white bodysuit was made of thin material that is easily tearable, so she could more easily use her Quirk. Nemuri had stated in an interview that she was trying varied materials to find out what works while adhering to costume regulations. In Vigilantes (and briefly in Chapter 24), she is also shown wearing stud earrings. The Vigilantes anime adaptation, and some colored artwork of its source material also depicts her with reddish-pink lipstick while in costume. During her years at U.A., Nemuri's hair was much shorter, having reached down to her chin. Her original costume was also much more revealing. Her breasts were covered by black protective plates, and she wore a dog collar, along with only undergarments, which were covered with a utility belt that held her whip. She was otherwise completely bare aside from an unbuttoned, high-collared trench coat. She also had large, angular shades, different from the mask she wears now. a very playful, flirtatious, and perverted person with an unpredictably serious and temperamental side to her. She got angry whenever someone interrupted her or insulted her, and, when it came to insults, she was especially sensitive about her age.

Nemuri had no shame for dressing or acting sexually in front of young students and appeared 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 excited to see the chivalry displayed by Eijiro Kirishima during the tournament when he shook Tetsutetsu Tetsutetsu's hand. Her love of "youth" was also a reason why she got angry when someone mentioned her age or called her old. Nemuri displayed her willingness to help her students by making sure they chose names that would represent themselves well. During the First Term 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 Minoru amazed her using tactical thinking to defeat her by luring her out and leaving her trapped in place before passing the gate.[6]

Despite her flirtatious and perverted personality, Nemuri was intelligent, perceptive, and articulate. For instance, in an interview, 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 response, Mt. Lady commented that Nemuri simply likes dressing the way she does for attention, and given her frequent posing while on TV or addressing the media, this in itself was quite likely. As shown during her time prior to working at U.A., Nemuri was capable of putting her lascivious hero persona to one side when off-duty. As a civilian, she was perfectly capable of presenting herself as an ordinary woman and displayed a caring, thoughtful, and even motherly side towards others. This was shown with her friendship and care towards Pop☆Step and her empathizing with Hina, despite the former's vigilantism and the latter's wrongdoings. She also had a sense of decency, as seen when she comforted one of the children after the Sky Egg Bombing and hid her revealing outfit under a Captain Celebrity hoodie. While acting bawdy and coming off as a hero who enjoyed her fame derived from her beauty and sex appeal, Nemuri was willing to fight and put her life on the front lines during the Paranormal Liberation War, demonstrating that, in spite of her excessive vanity, she held the true bravery and spirit of a hero. Similar to All Might and Shota Aizawa, she also believed in her students and their capabilities, acknowledging that all of them have what it takes to become great heroes in the future. Near the end of her life, Nemuri informed Momo Yaoyorozu that classes 1-A and 1-B must sedate Gigantomachia if he could not be stopped by force alone, encouraging her students to stop the behemoth's destruction, even if doing so broke the law, and trusted them to make the right call. As a Pro Hero and U.A. High School teacher, Nemuri was a highly tactful and formidable combatant. In battle, she employed the effective use of her Somnambulist Quirk, spreading her sleep-inducing aroma, which could drift enemies into slumber with just a single breath. Nemuri also used her costume and support gear to efficiently aid her Quirk. Despite only appearing as though it just fitted her dominatrix theme, her whips and fans were designed to pick up traces of her scent and launch it in any given direction, thus giving her Quirk more accuracy. This especially made her effective against enemies who rely on close-range attacks, as they would be rendered fast asleep without any sort of breathing device.

As seen during her First Term Final Exam battle, Nemuri enjoyed tormenting her opponents, which made her a frightening adversary to go against as well. Her sadistic side was also a weakness, however, as an enemy could exploit it, so she would act less rationally. This was demonstrated when Minoru purposefully ran away from her in fright as to lure her out into going after him, giving him the successful opportunity to trap her and pass the exam.