Noi has silver-white hair and red eyes. She is the fourth tallest character in the series and is very muscular. As a result, other characters are often unsure of their gender at first, until she speaks or takes off her mask. Her ears are pierced multiple times, with five piercings on each ear.
Usually, Noi wears a zip-up tracksuit with her name on it in several places, gloves, and sneakers, though she also has other outfits for formal occasions. She wears a blue gimp mask with an exposed "skeletal" mouth, like the Chatterer cenobite from the Hellraiser movies. The mask appears to have been patched with duct tape on top, similar to the tracksuit. She has duct tape around both their forearms and legs, including wrists and the calves.
Noi is very confident and carefree. So carefree that as Shin mentions, later on, she has stopped trying to avoid attacks because she can easily heal herself. Noi enjoys fighting and often competes with her partner Shin to see who can kill the most. Her bold personality can get them both into trouble because she doesn't bother to observe her surroundings carefully. The person she shows the greatest respect towards is Shin. She has a large appetite. She also enjoys fair fights and isn’t afraid of mostly any magic that comes its way.
Noi's power is healing, which is one of the rarest magic types. Her power is often used in the manga to heal Ebisu or the people that En turns into mushrooms. Thanks to her ability, Noi can heal herself quickly and without physically releasing the smoke. This makes her exceptionally resilient to physical attacks and virtually unkillable. She can also seemingly repair damaged objects, as seen when she healed Shins arm after it was melted, and seemingly restored his hammer to its original state.
Noi is En's younger cousin and only known relative, though which side of the family he comes from is unspecified. The circumstances to how and when she encountered En, and her life prior then are unknown. Since at a young age, En used his cousin Noi's powers for his business and schemes, making their relationship complicated. Even if En, in his own odd way, respects and cares for her, Noi hates him and has no respect for him.
According to En, he used to own the successful noodle soup franchise "Flower Smoke", which was around the time Noi was training for the Devil Exam. During their time as a bouncer in one of its restaurants, though they were not officially employed there, she met Shin. A thief with rotten arms, Noi caught him stealing food from the restaurant. She pursued him, confronting the thief and demanding to pay for what he stole. But Shin proposed a magic fight instead, offering only to pay if Noi managed to defeat him. To guarantee a fair fight and show Shin the nature of her magic, Noi healed his arms. Seeing as how her magic is not the kind used for fighting, Noi was about to suggest they fight with their bare fists, when Shin stabbed the back of her head with his hammer and ran away, promising to make up for what it did for him, and leaving a bleeding and angry Noi on the floor to heal.
At some point during her childhood, Duston, a powerful Devil, approached her due to her rare magic with the chance to take The Devil Exam, so that she could become a Devil herself. After a short time of training, she was the last remaining applicant, since all the rest were killed in various manners, such as by giant bats, suicide or getting accidentally killed by Duston. To make her body morph into that of a Devil, Noi used to wear heavy, impractical armor almost all of the time. As one of the effects of the Devil transformation, her personality was warped, causing her to become a carefree, violent, and spoiled brat. She was already far along in her exam when she decided to sacrifice her devilhood.
Time passed, and Shin was hired by En to become one of his cleaners due to his mutilation type of magic. He and Noi became close friends, beating people up for En and talking about how dumb he was because of his business ideas, an example being a jingle composed and interpreted all by himself for his restaurant. On the day of Blue Night, they got ambushed and separated by two shady Magic Users named Baku and Yaku, who wanted to beat them unconscious. They desired to kidnap them both to force them to sign the contracts making them their partners, since contracts signed on the Blue Moon Night forces a person to do what their partner says unquestioningly until the contract gets renewed. Though Noi was not allowed to use any magic, as she was in the last step of her exam with horns and tail already, they fought and seemingly killed their aggressors. Noi killing Baku by crushing his head with a boulder. But not before the beheaded corpse of Baku managed to shoot a barrage of smoke in her direction. Shin took the the hit, flaying his back in the process. Shin told Noi not to heal him, so that she could become a Devil and finally make up for what she did for him before by treating his arms and thereby giving him a chance to live. With no regrets, Noi decided to relinquish her devilhood to save him, as Duston appeared to tell her the exam was over, and she lost her chance. Despite that, she and Duston are still really good friends today, and since that day, Shin and Noi became partners.
Noi appears for the first time in the fourth chapter of the manga, during a cleaning mission with its senpai Shin. With brute force, she kills some of the remaining Cross-Eyes members in a hideout to take an elderly unnamed Cross-Eyes to En. Nothing more than a head, the target is put in a cheap body bag and accidentally splashed all over Noi, to her disgust and Shin's annoyance. Subsequently, they meet En at a restaurant, who is dressing for the event (Noi uses a tight short leather dress with needles at the end). En entrusts them the mission to find and kill Kaiman and Nikaido (Due their Magic User hunts in Hole, they killed Matsumura and injured Fujita, now present in the dinner with Ebisu, another of Kaiman victims).
Leaving to Hole at the Day of the Living Death, they find them and engage in a fight. Noi is surprised by Nikaido skills and even asks her to be her friend, but remembers that she had to kill her anyways. After a tied fight, she overpowers Nikaido and almost kills her. Seeing that Shin beheaded Kaiman, she opens a Magic Door and escapes. The cleaners come back to the sorcerer's realm believing that Kaiman survived somehow and that they need to find him. Noi is among the rest in turkey's house to make a doll of "The man inside the lizard head", following the doll through the city until they find a box inside an old building, where the doll went berserk. It almost kills Fujita and Ebisu. Noi nurses the two while Shin destroys the doll, then they open the box to reveal a rotten head. Noi fixes it with her magic, showing that the head belonged to "The man inside the lizard head mouth".
- Can't walk in high heels
- Seems to favor leather clothes or form-fitting wardrobe.
- Noi's name (能井) uses the kanji for Talent or Ability (能) Nō and the kanji for Town or Community (井)