Seo Himezuka possesses a half-British, half-Japanese heritage and relocated to Japan at age 17. Witch blood from the Himezuka Clan grants him an enduringly youthful and beautiful appearance despite his 38 years, frequently causing him to be mistaken for a woman—a point of irritation amplified when his colleague Kyoichi Sakaki uses his picture to end relationships.

He first met Reiji Senda during an early temple visit, assisting Reiji with a supernatural obstruction caused by a kitsune spirit. This established their dynamic, with Seo acting as Reiji's "eyes" for perceiving occult phenomena. Their investigative partnership continued until both joined the Nocturnal Community Relations Division approximately 15 years later.

As a member of the Himezuka Clan, one of the "3 Power Clans," Seo lacks innate spiritual abilities but is a genius inventor. He develops tools like the Ibn Ghazi spray, which renders invisible supernatural entities ("Anothers") visible to humans, and specialized barrier tape for containment and protection. His inventions see widespread adoption across regional divisions.

A significant trauma arose when he discovered inventions he created for his clan were used to torture and kill Anothers beneath the Himezuka estate. This led him to live independently in an apartment, distancing himself from the main household. Within the division, he operates as a methodical problem-solver, often exhibiting enthusiasm when encountering new supernatural phenomena like a colleague's "Ears of Sand" ability. His analytical approach and inventions consistently support the team's missions, reinforcing his role as a pragmatic and resourceful contributor.