Beatrice Lambert, known as Beth, is an American graduate student delving into the Hiraga bloodline's curse and its link to immortality. She aids Gen Hiraga in investigating his family's history after he moves into his grandmother's house and suffers recurring dreams tied to his ancestors' tragic ends.

Her involvement triggers Gen's fragmented memories and intensifies his unraveling inner turmoil as they expose the clan's secrets. Beatrice possesses psychic abilities and exhibits vampiric traits, physically characterized by gray hair cut to ear length, red eyes, and consistent use of hair ribbons. She serves in a domestic capacity as a maid.

Her background connects to the supernatural aspects of the Hiraga curse, specifically the whispered legend of immortality encoded within the family genes. Their investigation uncovers ties between Beatrice and a mysterious woman from Gen's dreams, though the precise nature of this connection remains a central enigma.

Beatrice reappears in the sequel "Zoku Gosenzo Sane," maintaining her association with the story's supernatural elements. She functions as both a catalyst for Gen's discoveries and a conduit to the occult dimensions within the Hiraga lineage's secrets.