Maremi Gekkōin originated as a human college student. A profound fixation on the vampire Adam consumed her after she misinterpreted his flirtation with her friend as intended for her. This sparked persistent stalking, prompting Adam's repeated attempts to evade her. A critical moment arose when Maremi pushed Adam from the path of oncoming traffic, sacrificing herself. In gratitude for this selfless act, Adam saved her life by biting her, transforming her into a vampire.

Her transformation triggered significant physical changes. As a human, she possessed wavy brown hair swept right, freckles across her nose bridge, oval-shaped glasses obscuring her eyes, and wore casual attire including a pink jacket and navy-blue pants. As a vampire, her hair gained more pronounced volume with lifted bangs, her ears and teeth became pointed, and she frequently manifested large bat wings enabling flight. She adopted a dark-blue split dress and heels. Her posture and demeanor shifted to project greater confidence, with her eyes becoming visible behind her glasses in some depictions.

Upon awakening, Maremi declared herself the "Vampire Empress," stating she felt radiant and had "returned to her true form." This declaration, coupled with an immediate display of exceptional power, hinted at a latent suitability for vampirism. Her abilities focused on flight via her bat wings, though her overall strength suggested broader vampiric capabilities.

Her personality underwent marked evolution. Initially delusional and obsessively pursuing Adam, her near-death experience and transformation fostered self-acceptance and confidence. While retaining affection for Adam, she ceased defining herself solely through him, adopting a calmer, more commanding presence. Adam, in turn, became willingly devoted to her, seeking self-improvement to become "her equal."

Her character arc challenges specific anime tropes. Her initial design incorporated stereotypical elements for "unattractive" characters (obscured eyes, exaggerated features), yet her post-transformation appearance signifies inner confidence rather than conventional beauty or weight loss. Her happiness and power manifest without conforming to thin ideals, stemming from self-actualization, not Adam's validation.

The name "Maremi" combines the kanji for "hope" (希) and "beautiful" (美). "Gekkōin" translates to "moonlight temple," with the "in" (院) suffix historically associated with emperors and empresses, connecting directly to her self-proclaimed title.

Her known relationships center primarily on Adam.