Hitomi Mochida is introduced as a childhood friend of the main protagonist, Asumu Adachi. She is a central figure in his civilian life, beginning the series as a fellow student preparing for their high school entrance examinations alongside Asumu and their mutual friends.

In terms of personality, Hitomi is characterized by her gentle, caring, and feminine nature. She is consistently portrayed as a kind and polite young woman who looks out for her friends when they appear to be in trouble, often offering comfort and support. Her feelings for Asumu are a key aspect of her motivation; she harbors a romantic crush on him and actively seeks his attention. However, Asumu remains generally oblivious to her overtures, which is a source of personal frustration for her.

Hitomi's primary role in the story is tied to Asumu's growth and his life outside of the world of the Oni, the series' heroes who fight monsters called Makamou. While she is aware of the Tachibana sweet shop and its connection to Hibiki and the other Oni, her involvement with the supernatural elements of the plot is minimal. Her narrative importance is largely horizontal, existing alongside Asumu as he navigates the challenges of adolescence, rather than being directly involved in the battle against the Makamou. Her school life, including initially being a cheerleader and later engaging in a paper play, forms the backdrop for her interactions with Asumu.

Her key relationships include her friendship and romantic interest in Asumu Adachi. She also becomes acquainted with other characters such as Akira Amami, whom she initially sees as a potential rival for Asumu's affections but later becomes comfortable with upon understanding that Akira does not view Asumu romantically. She interacts with the members of the Tachibana shop, knowing them as acquaintances of Asumu.

A notable aspect of her character development is how she was affected by changes in the series' production. Following a change in the scriptwriter around episode thirty, several elements of her character shifted. Her consistent presence and significant role as a heroine diminished, and some of her established activities and motivations were altered or dropped, such as her background in cheerleading. Her portrayal became less prominent, and her potential for further development was curtailed. Hitomi Mochida does not possess any supernatural abilities or combat skills, remaining an ordinary human civilian throughout the series.