Eiko Hozuki is a first-year university student and a central figure in the narrative, serving as a crucial emotional anchor for the group. Her background is defined by a traumatic spiritual encounter during childhood alongside her childhood friend, Keitaro Gentoga. This event left both of them cursed, manifesting as nerve endings that grew from their hands, with Eiko bearing the curse on her left hand. This experience, while deeply frightening, also instilled in her a fascination with the occult and folklore, which she later decides to formally study to better comprehend the supernatural dangers Keitaro faces.

Personality-wise, Eiko is a complex individual whose outward cheerfulness and academic diligence mask a much darker interiority. Her most defining trait is her deep, long-standing love for Keitaro, which has morphed into a twisted and obsessive fixation. She displays an extreme and overprotective nature, engaging in intense stalking behaviors to monitor his safety. This includes wiretapping his phone, placing hidden cameras in his environment, and using GPS trackers to follow his movements and even monitor his vital signs without his knowledge. Despite this disturbing side, she is genuinely intelligent, earning excellent grades in her studies while also possessing a strong foundation in computer science, which she applies to her surveillance activities. She is also noted to be very similar to her young cousin, Yayoi, in her borderline lustful fascination with ghosts and the macabre, though she does not share Yayoi or Keitaro's ability to sense spirits.

Eiko's primary motivation is the protection and possession of Keitaro. Her actions are almost exclusively driven by her desire to keep him safe and to secure his affection. She facilitates his return to society after his shut-in period and actively introduces him to her cousin, Yayoi, as a tutoring job, which inadvertently draws him deeper into the world of spirit hunting. Her role in the story is primarily that of a supportive, though morally ambiguous, ally. While she lacks the psychic powers and strategic genius of Yayoi or Keitaro's spiritual magnetism, she provides logistical support, research, and a normal human perspective, even as her own actions are far from normal. She joins Yayoi and Keitaro on trips to haunted locations, driven by her love for Keitaro and her own interest in the occult.

Her key relationships are with Keitaro and Yayoi. Her relationship with Keitaro is the core of her character; she is his self-appointed guardian and stalker, and he reciprocates a mutual affection for her, despite her methods. Her dynamic with Yayoi, her younger cousin, is notable for its contrasts. While Yayoi is a stoic and genius child ghost hunter, she herself finds Eiko's stalking behavior to be creepy, though she pragmatically comes to approve of it because the surveillance equipment provides valuable information and protection for Keitaro, which in turn aids Yayoi in her own mission. Eiko also develops a relationship with Ai Kamiyo, Keitaro's second student, as part of the expanding group.

In terms of development, Eiko remains fairly static in her core obsession, but her role evolves from a concerned childhood friend reintroducing Keitaro to society to an active participant in dangerous supernatural expeditions. Her skills in computer science and her research into folklore become more directly useful as the story progresses, even if her primary method of contribution remains her unyielding desire to be near Keitaro no matter the risk. Notably, her character serves to complicate the moral landscape of the series, as her devotion to Keitaro is portrayed not as purely wholesome, but as a dark, possessive love that is both a source of strength and a potential concern. Her notable abilities are not supernatural but practical: she has a high level of intelligence, excels in computer science and surveillance, and is a diligent student of folklore, all of which she uses in her quest to understand and protect Keitaro.