Hinako is the youngest of the twelve sisters who live with her older brother. As a child of kindergarten age, her small stature and youthful demeanor are among her most defining traits. She has a bright, cheerful, and highly energetic personality that often brings a sense of liveliness to her surroundings, which stands in stark contrast to the more reserved nature of her similarly-aged sister, Aria. Her behavior is very much that of a young child; she is prone to tears when upset and has a stubborn streak that can emerge when she does not get her way. One of her most endearing quirks is her unique manner of speech, as her young age affects her pronunciation. This is most notable in how she addresses her brother, whom she calls "Onii-tama" instead of the standard term.

Hinako’s motivations are simple and centered entirely on her affection for her older brother and her enjoyment of a childlike world of play and fantasy. She seeks out his attention and company, often asking him to read storybooks to her, as this is one of her favorite activities. Her love for her brother is pure and free of the complicated romantic feelings that some of her other sisters harbor. While she speaks of marrying him one day, this is framed as an innocent, childlike promise for the future rather than a serious romantic pursuit. In one notable instance, when she loses her treasured teddy bear, her brother helps her search for it. Ultimately, she declares that as long as he is with her, she needs nothing else, demonstrating the depth of her reliance and adoration.

In the story, Hinako’s role is often to provide moments of innocent warmth and comic relief. Her young age means she is less involved in the more dramatic or romantic storylines than her older sisters. However, her imagination plays a key part in some episodes, such as when she goes on a fantasy adventure on a rainy day. In this daydream, she encounters a frog prince but remains steadfast in her quest to find her brother, the person she loves most. In another instance, she participates in a school play, taking on the role of Little Red Riding Hood, where her spontaneous and adorable actions help salvage a performance.

When it comes to relationships, her bond with her brother is the most significant, serving as the anchor for all her actions. The information available does not go into great detail about her daily interactions with the other sisters, though she is often seen in the company of Kaho and Aria, the other youngest members of the group. Regarding her development, Hinako shows very little change over the course of the story. This is consistent with her role as the youngest sister; the narrative focuses on preserving her innocence and childlike wonder rather than leading her toward emotional maturity. While she occasionally demonstrates a more mature perspective than her age would suggest, she largely remains the same cheerful and playful little girl. Her notable abilities lie in her rich imagination and her capacity to bring fantasy into her everyday life, weaving fairy tale elements into her real-world experiences. Her distinctive laughter is also described as quite unusual, sounding like "kushishishi".