Naon Yuno is a supporting character in the anime and manga series Chained Soldier, known in Japan as Mato Seihei no Slave. Originally a human, she was a successful and elegant fashion model in the human world before a catastrophic event known as a Mato disaster transported her into the dangerous alternate dimension called Mato. To survive an attack by the monstrous Shuuki, she ate a Peach, a fruit that grants superhuman abilities exclusively to women. However, the Peach did not simply grant her powers; it physically and mentally transformed her into a humanoid Shuuki, a demon-like being with horns and other supernatural traits. After this transformation, she fled from the Onmyou Agency, a government organization that captured and experimented on individuals like her, and later found refuge with a group of other humanoid Shuuki led by Aoba Wakura.

In terms of personality, Naon Yuno is defined by an intense and unwavering obsession with beauty. She frequently uses the phrases beautiful and not beautiful as verbal tics, judging people, objects, and situations based on her own high aesthetic standards. This fixation extends to her own appearance, and she is constantly seeking ways to become more beautiful, even in her monstrous form. She is elegant and composed in demeanor, carrying herself with the poise of her former career as a model. Despite her obsession, she is also precocious and intelligent, and she can be fiercely loyal to those she considers allies. Her motivation is driven by a desire to pursue and protect beauty in all its forms, and this serves as her personal philosophy and guiding principle in both combat and daily life.

Her role in the story is as a member of Aoba Wakura's faction of humanoid Shuuki who have forged a truce with the Mato Defense Force. She fights alongside Aoba and other humanoid Shuuki like Koko Zenibako, serving as a capable combatant and a close companion to Aoba. Her relationship with Aoba Wakura is one of deep loyalty and friendship, as Aoba leads and protects the humanoid Shuuki who have been mistreated by human authorities. Naon also interacts with members of the Mato Defense Force, though her past imprisonment and experimentation make her wary of organizations like the Onmyou Agency. Her key relationships include her bond with Aoba, as well as her connection to the other humanoid Shuuki who share her fate of being transformed and outcast.

Throughout the story, Naon Yuno experiences development as she becomes more integrated with the Mato Defense Force and learns to trust humans again, particularly through her interactions with the main protagonists. Her journey involves reconciling her past as a human with her current existence as a humanoid Shuuki, and she grows from being a victim of circumstance into a proactive fighter who uses her abilities to protect her newfound family. Her notable ability is called Hidden Beauty, which allows her to become intangible, enabling her to hide within or pass through solid objects and even other living beings. This power makes her an effective spy, scout, and evasive combatant, allowing her to phase through attacks and move unseen. She also retains the physical characteristics of an oni, including horns and a slender, beautiful figure, and she can command ordinary Shuuki due to her humanoid Shuuki nature.