Hatsumi Mataki is the local physician and aunt of Shoko Mataki. She acts as Eiri Kurahashi's primary medical caregiver, examining his unexplained physical injuries and psychological symptoms. Her rational, science-based perspective leads her to eliminate physiological causes for Eiri's deteriorating condition, particularly his hallucinations and psychosomatic wounds. This clinical approach clashes with supernatural interpretations offered by others.

She shares a close friendship with Zenshinni of Shakado while maintaining professional concern for Eiri's well-being. Her medical expertise proves inadequate when confronting phenomena like Shoko's coma, which lacks any identifiable scientific explanation. Hatsumi's inability to diagnose or treat these occurrences highlights the limitations of conventional medicine. Her role underscores the conflict between empirical rationality and emerging supernatural forces.