Mitsuki's older sister, Hazuki, is in a zombie state due to a salivary gland parasite infection; her skin has turned a dull green and her nails have grown sharp. She has light brown shaggy medium-length hair and wears a black-and-white striped knit hat with bear ears and black star ornaments on the strings. Her eyes are marked with a spiral pattern (🌀), and her mouth is filled with shark-like fangs. Her outfit consists of a black short-sleeved T-shirt with a monster bear print layered over striped long sleeves, paired with oversized shorts and striped long stockings. Lore-wise, the cause of Hazuki's transformation is an undiscovered parasite that lives in the salivary glands and manipulates brain waves. Her behavior of constantly approaching to lick and hug her sister despite not recognizing her was not out of affection, but an instinct induced by the parasite to spread the infection. She is the only zombie without aggression, but her intelligence has regressed to that of an infant, barely able to speak simple words. When the anthelmintic administered by Mitsuki kills the parasite, the biological reactions sustained by the parasite shut down, the spirals in her eyes vanish, and her body turns cold, returning her to a true corpse.

The protagonist and researcher, Mitsuki is Hazuki's younger sister. She has green side-twin-tail hair adorned with yellow bear-shaped hairpins. She has transparent green eyes and is neatly dressed in a white lab coat over a black dress shirt and tie. Lore-wise, Mitsuki is not a simple human but an android who has been manufactured and repaired multiple times. In the music video, identical Mitsuki units are seen maintaining themselves with tools. Her cry of "I can't even shed tears...!" when Hazuki dies indicates her physical inability to cry due to her mechanical body. To cure her sister, she identifies the undiscovered parasite and develops an anthelmintic, but the medicine turns her sister—who was only clinging to life through the parasite's power—into a true corpse, leading to the cruel tragedy of causing her sister's final death with her own hands. She does not understand that her sister's instinct to infect her with saliva is not a display of affection, nor does she realize that the vaccine is actually a lethal injection for her sister.