Otsu Sawatari, a 24-year-old medical graduate student, navigates his undead existence by leveraging his academic position to discreetly investigate autopsies and zombie-related incidents. His crew cut, tinted sunglasses, and sharp smart-casual wardrobe lend him an intimidating air, causing many to assume ties to organized crime—a stark contrast to his reputation as a top-tier academic performer.

In confrontations, he channels ectoplasmic flames that engulf his fists, blending supernatural prowess with clinical precision. Though colleagues recognize his methodical, grounded approach to unraveling undead mysteries, his role remains peripheral to the central narrative. Chika, a frequent associate, teases him with the nickname "Ossan," a jab at his stern demeanor, yet shifts to the formal "Otsu-san" in professional settings—a duality underscoring his layered interactions. His personal history and broader narrative contributions outside core storylines remain unelaborated, with documented accounts prioritizing his expertise, tactical combat style, and operational dynamics within the series' structure.