Hijiri Sanagi

No, she isn't actually emotionless—she just puts up a heavy, stoic front to defend herself.
Before Kengo enters her life, Sanagi presents a deadpan, distant, and cold exterior to the world. She wears her oversized clothes, scarf, and massive headphones specifically as a wall to keep people away. To anyone looking from the outside, she seems completely detached, silent, and aloof.
However, beneath that surface, she is actually driven by intense, volatile emotion:
Overwhelming Fear and Anxiety: Her stoicism isn't a lack of feeling; it's a defensive freeze response. Her scopophobia causes her deep psychological agony and terror whenever she feels perceived by others.
Resentment and Defiance: She harbors a bitter, burning frustration toward normal society and the expectation that she should "fix" herself or fit in.
Desperate Loneliness: Beneath her hostility is a profound, aching sorrow over her isolation.
Her cold demeanor is an armor, not a personality trait. The moment she realizes Kengo's presence doesn't trigger her crippling anxiety, that cold front shatters pretty quickly—revealing a girl who is stubborn, emotionally intense, fiercely possessive, and desperately hungry for connection.

Hair and Build: Sanagi is drawn with a petite, fragile frame that emphasizes her vulnerability. She has short, slightly unkempt hair—often depicted as a pale, ashy gray or light blonde in color illustrations. Her bangs frequently fall into her eyes, creating a natural veil that helps her avoid direct eye contact with others.
The Headphones: Her most iconic visual trait is a pair of large, over-ear headphones. She wears these almost constantly, regardless of whether she is actually listening to music. Visually, they function like her own personal A.T. Field—a literal and psychological barrier designed to block out the intrusive noise of society and signal to others that she is completely unapproachable.
Bundled Clothing: True to the cold, wintery atmosphere of the story, Sanagi is rarely seen without heavy layers. She typically wears an oversized jacket and a thick scarf wrapped high around her neck, often burying the lower half of her face in it. This isn't just for the cold; it's a physical manifestation of her scopophobia, allowing her to hide as much of her body and face from the public gaze as possible.
Facial Expressions: Her default expression in the manga is deadpan, guarded, or glaring. Because she is terrified of being looked at, she often stares downward or averts her gaze defensively. It’s only when she is alone with Kengo—the one person who doesn't trigger her phobia—that the manga softens her expressions, showing rare moments of warmth or genuine teenage frustration.

The Portable Bubble: Headphones and Defenses
Because of her scopophobia (fear of being looked at), the outside world is an agonizingly loud, judgmental, and terrifying place. To survive in public, Sanagi creates a "portable environment" using large, over-ear headphones. She constantly wears them not necessarily to listen to music, but to signal to others that she is unavailable and to muffle the sensory input of the world around her. She bundles herself up to hide her face and body as much as possible, effectively carrying her isolation with her wherever she goes

Her social environment is virtually non-existent.
School: She is a high school dropout, having entirely abandoned the primary social environment expected of a 17-year-old.
Family: She is estranged from a normal family dynamic. Her grandfather is her caretaker, but their relationship is highly transactional and distant—he literally pays Kengo to be her "friend" and keep an eye on her, rather than engaging with her deeply himself.
Friends: Before Kengo, she has none. She has entirely removed herself from the social ecosystem

Severely Avoidant and Defensive: At the start of the story, Sanagi is entirely withdrawn. Because of her scopophobia—an extreme, debilitating anxiety over being looked at or making eye contact—she adopts aggressively anti-social behavior to push people away and purposely avoid human interaction, which leads to her dropping out of high school. 
Fiercely Stubborn and Decisive: While she appears fragile to the outside world, Sanagi possesses an iron will when it comes to the things she cares about. When Kengo attempts to distance himself or make decisions she disagrees with, she pushes back aggressively. At one point, she goes to the extreme length of locking both of them in a freezing container just to convince Kengo not to undergo treatment to remove the parasite. 
Intensely Pragmatic About Happiness: Perhaps her most defining philosophical trait is how she handles the revelation that her feelings of love might just be the artificial side effect of a parasite. While Kengo is distressed by the idea of a "puppet love," Sanagi is entirely unapologetic and pragmatic about it. Her stance is highly defiant: she argues that she doesn't care if her love is a "sham" or an illusion created by a worm, because the parasite taught her how to like people and gave her happiness she couldn't achieve on her own. 
Deeply Dependent: Because Kengo is the only person she can interact with comfortably, she becomes intensely attached to him. Her personality shifts from isolating herself from the world to fiercely guarding the small, isolated world the two of them build together.

A 17-year-old high school girl who refuses to go to school because she suffers from scopophobia, which is an excessive, paralyzing fear of being stared at by others. 

Interests: She has a distinct fascination with parasites.Personality: Isolated and cynical, she believes that everyone around her looks uncomfortably happy.

Hijiri Sanagi’s environment in Parasite in Love is a physical and psychological manifestation of her severe isolation. She exists in a modern Japanese setting, but she experiences it through a lens of intense fear and detachment.
Her environment can be broken down into a few distinct layers: