Haruka Shigure is a 15-year-old (later noted as 16) human student at Miyasaka High School. She has shoulder-length brown hair with distinctive purple tips and deep sky-blue eyes, typically wearing the school uniform: a lavender pink skirt, matching pink blouse, and a yellow ribbon. A member of the tennis club, she shares a longstanding connection as Taito Kurogane's childhood friend and classmate.

Her sweet, caring, and affectionate demeanor is especially directed towards Taito. She demonstrates her well-documented romantic feelings through daily actions like preparing elaborate lunches, comfortably waking him from class naps, or dabbing away food from his face without concern for gossip. She consistently prioritized his well-being, supporting him emotionally and physically during his recovery from a past karate injury. However, the arrival of Saitohimea, Taito's deeply connected vampire companion, triggers intense jealousy and insecurity in Haruka. Witnessing their profound bond and Himea's physical closeness causes her significant emotional distress, a challenge her friends acknowledge despite recognizing Haruka's own attractiveness.

Haruka experiences unexplained dissociative episodes involving complete mental lapses, finding herself in locations with no memory of arrival. During these episodes, an alternate personality surfaces, marked by physical changes: her hair darkens and her eyes shift to golden-yellow. This observer personality gathers intelligence on Saitohimea and Taito without their awareness for espionage related to Himea's powers and activities. The origin of this implanted personality, whether linked to factions like the Tenma, the Military, or the Church, remains undisclosed.

Beyond the romantic subplot, Haruka is intrinsically linked to the series' lore as a physical manifestation of one half of the split entity Ramiel Lilith, with Saitohimea constituting the other half. This connection positions her within a broader supernatural prophecy concerning the world's potential destruction.