Mamoru Sakazaki is a teacher at Hijirigasaka Academy, where he serves as the homeroom instructor for Basara Toujou and the other students in class 1-B. He is portrayed as a benevolent and caring figure who is well-liked by his pupils, who affectionately refer to him as Mamo-chan. His motivations in his professional role appear to be genuine concern for his students' well-being and maintaining a supportive classroom environment.

However, this public persona conceals a manipulative and predatory nature. In flashback sequences revealed during the series, it is shown that Sakazaki used his position of trust to coerce female students into sexual acts against their will. His true character is exposed through the testimony of Chisato Hasegawa, a fellow teacher, who recounts that Sakazaki attempted to assault her. Before the events of the main story, he was killed by the god Ornis; in the light novel, Ornis specifically targeted him because of his unwanted advances toward Chisato, who is later revealed to be the god Afueria.

Sakazaki plays a minor role in the narrative, appearing only in flashback and exposition. His function in the story is to illustrate the hidden dangers that existed at Hijirigasaka Academy and to provide backstory for Chisato Hasegawa's character, explaining her guarded nature and her connection to the supernatural world. He has no direct relationship with the protagonists in the present timeline, as he is already deceased when the series begins, and his interactions with them are limited to their former student-teacher dynamic. His death at the hands of Ornis also serves to establish the power and ruthlessness of that antagonistic force.

Mamoru Sakazaki possesses no supernatural abilities. His influence in the story stems entirely from his social position as a teacher and the trust he was able to exploit before his death.