Beniko Zashiki is a student at Hyakki Academy, belonging to Class 2-3. She is a yokai known as a zashiki-warashi, a household spirit traditionally said to bring good fortune and prosperity to the home where she resides. Her existence as a yokai was born from the love and care invested in a place; specifically, she came into being after her three human fathers, Matsuo, Toratake, and Koume, purchased and renovated an old house, transforming it into a guest house. Raised by these three men, to whom she is not related by blood, she feels a deep sense of gratitude and loyalty. She is aware that her presence inadvertently caused one of her fathers to lose a girlfriend, and this has strengthened her resolve to bring them happiness and become a daughter they can be proud of.

In terms of personality, Beniko is often portrayed as aloof, blunt, and mischievous. She has a sharp tongue and a rebellious spirit, frequently using her words to tease or provoke those around her, particularly her classmate Kotaro Hijita, whom she often makes cry. She is fiercely independent and is not easily swayed by the opinions of others. Despite her rough and boyish exterior, which leads fellow student Mikoto Sano to not treat her in a girly way, she possesses a strong sense of loyalty and cares deeply for her friends and family, even if she expresses it in an indirect manner. She has a strong competitive streak and tries to hide her softer emotions, though these feelings can sometimes be betrayed by a visible blush.

A defining trait of Beniko is her intense passion for video games. Her journey into becoming a dedicated gamer began during her first winter at Hyakki Academy when she borrowed a game from Kotaro Hijita. This hobby quickly became an all-consuming obsession, leading her to skip classes and become a shut-in, spending most of her time holed up in her dormitory room. Her truancy became so severe that she was at risk of having to repeat a school year. It was through the persistent persuasion of her teacher, Haruaki Abe, that she was convinced to return to school, though she continues to struggle with punctuality and is often late to class.

Beniko possesses abilities inherent to her nature as a zashiki-warashi. The most prominent of these is her influence on fortune and misfortune, which is directly tied to the color of her clothing. While she normally brings good luck, wearing the color red reverses this effect, making her a harbinger of bad luck. Despite this, she deliberately wears a red tracksuit, often under her school uniform, as an act of defiance and to annoy her teacher, Haruaki Abe. Another supernatural ability she has is the power to make herself, other people, or objects around her become invisible. Beyond her yokai powers, Beniko is highly skilled with computers, excelling in programming and the ability to manipulate online information.

Her key relationships are central to her character. With Haruaki Abe, she shares an uneasy and teasing dynamic, taking joy in flustering him and openly flouting the rules by wearing her red tracksuit. However, she also responded to his efforts to help her, acknowledging his role in getting her back to class. With her childhood friend Kotaro Hijita, her teasing is a constant, but their shared history is significant; it was from him that she first borrowed the game that sparked her gaming obsession. She shares a practical and friendly rapport with her classmate Mikoto Sano, with whom she works together to secure bread from the student store. Throughout the story, Beniko's primary development arc involves her struggle to balance her reclusive gaming habits with her responsibilities as a student and her relationships. While she continues to be a passionate gamer, her return to school life, prompted by her teacher, marks a shift away from complete isolation. Her underlying motivation remains her deep-seated desire to make her three fathers proud, driving her to participate more in school and family life despite her natural inclination toward solitude and mischief.