Noi is an elite magic-user who works as a cleaner for the En family alongside her longtime partner and closest friend, Shin. She is the older cousin of En, the head of the family. Physically, she is notably tall and muscular, with silver-white or pale blonde hair and red eyes, which leads many to speculate that she may be albino, though the story never explicitly confirms this. She is the fourth tallest character in the series, and her imposing stature, combined with her mask, often causes others to be uncertain of her gender until she speaks or removes it. Her mask is dark blue, made of a vinyl-like material, and is more form-fitting than Shin's, featuring a zipper. She also has several ear piercings and medium-length wavy hair. In her past, she was of a more normal physique, but her body grew larger over time as she trained alongside Shin.

Personality wise, Noi is confident, cheerful, and carefree. She approaches combat with enthusiasm and a love of fighting, often competing with Shin to see who can defeat more opponents. Her confidence in her own abilities is so great that she has been known to stop actively avoiding attacks, knowing she can heal herself easily. She is direct and straightforward, guided by her own sense of fairness, as demonstrated when she first met Shin. At that time, Shin was a thief with cursed, rotting arms, and instead of punishing him, Noi healed his arms first to make the fight fair before challenging him to a magical duel. This encounter set the foundation for their deep partnership.

Noi's motivations are rooted in loyalty to Shin and to the En family. As a cleaner, she is responsible for eliminating threats to the family, and she carries out this role with brutal efficiency. However, her loyalty is tested over the course of the story, revealing emotional depth beyond that of a simple enforcer. She gradually develops a more independent stance while never fully abandoning her allegiance to En.

Her most defining relationship is with Shin. They function as complementary opposites: Shin's magic dismembers and dissects, while Noi's heals. Their bond is one of the central emotional anchors of the story, and she is shown to care for him deeply, once reviving him from a reptile-like state with her powers. Her relationship with En is one of family and obligation, as he relied on her healing abilities from an early age.

Noi's notable ability is her smoke magic, which can heal almost any injury, including regenerating severed limbs and destroyed organs. The only limit is that it cannot reverse true death. This makes her both a fearsome combatant and an invaluable strategic asset for the En family, as she is simultaneously a frontline fighter and a support healer, a rare dual role in the series. At one point, she temporarily disabled her healing power in order to train pure physical combat, demonstrating that her formidable strength is not dependent on magic.