Hakuu is a lady-in-waiting in the service of the Empress Gyokuyou in the anime and light novel series The Apothecary Diaries. Her background is deeply intertwined with that of her mistress; she grew up in the Western Capital as a member of the Yi Clan and was a childhood friend of Gyokuyou. Her early life was marked by political turmoil, specifically a rebellion against the Yi clan. When she was around five years old, she, along with her mother, her two younger sisters, and a boy who would later be known as Rikuson, was forced to evacuate and hide in the house of Gyokuyou's mother to escape the supporters of a man named Gyoku-ou. This period of conflict and displacement shaped her early years and her fierce loyalty to Gyokuyou.

Physically, Hakuu is one of three nearly identical sisters, the other two being Kokuu and Sekiu. To distinguish herself as the eldest, she wears a white ribbon in her hair, while her sisters wear black and red ribbons respectively, as their names translate to 'white feather', 'black feather', and 'red feather'. Maomao has described the sisters as having almond-shaped eyes and eyebrows that resemble drawings in charcoal.

Hakuu's personality is defined by her protectiveness and serious, mature demeanor. She is highly protective of Gyokuyou and deeply cares for her well-being, which makes her distrustful of anyone she perceives as trying to take advantage of the Empress, including Gyokuyou's own relatives such as Gyoku-ou and Gyokuen. Among Gyokuyou's ladies-in-waiting, she is considered one of the most mature and serious, second only to the head lady, Hongniang. This seriousness manifests as a critical eye; for instance, she openly criticized Gyokuyou's carefree attitude when Maomao was summoned to investigate a damaged hairpin belonging to the Empress.

Her role in the story is primarily that of a trusted and capable lady-in-waiting to Empress Gyokuyou. She and her sisters join the Jade Pavilion as new attendants, taking on various duties including cleaning and cooking, and are a consistent presence in the Empress's household. Beyond her domestic duties, Hakuu plays a key role in a secret network of communication. She was responsible for sending Gyokuyou's letters via pigeon to Rikuson, who now lives under a new identity. Through this action, she urges Rikuson, a fellow survivor of the Yi clan's downfall, to return to the Western Capital and assume a leadership role among their people. This demonstrates her ongoing commitment to her clan's legacy and her strategic thinking.

Hakuu's key relationships are central to her character. Her most significant bond is with Empress Gyokuyou, whom she serves with unwavering loyalty and protectiveness. She also has a notable, if complex, relationship with Rikuson; they knew each other as children when they were both survivors sheltered together, and as adults, she recognizes and contacts him, leveraging their shared past for a political purpose. Her relationship with her two younger sisters is also a defining trait, as the trio functions as a unit within the palace, working alongside the other ladies-in-waiting.

Regarding her development, Hakuu is depicted as someone who has grown from a child survivor of a violent political purge into a strategic and mature adult. Rikuson observes that in the decade since they last met, she has become a loyal lady-in-waiting to Gyokuyou, yet she still seeks to restore the Yi clan to its former power. This shows she has not abandoned her past but rather integrated it into her current life of service. Her notable abilities include being diligent and perceptive, having demonstrated her capabilities by taking care of Maomao and being recognized for her intelligence even at a young age. Her most significant skill, however, is her ability to operate discreetly within the palace, managing a covert line of communication that even the Imperial family was unaware of.