Hazuki Yuiga is a supporting character in the series, known for being one of the younger sisters of the protagonist, Nariyuki Yuiga. She is specifically the younger sister of Nariyuki and Mizuki Yuiga, as well as the older twin sister of Kazuki Yuiga.

Hazuki is a young elementary school student, distinguished by her hairstyle which she wears in pigtails. Her nickname is Ha-chan. In terms of personality, she is noted for being cute alongside her twin brother, Kazuki. She and her brother enjoy teasing their older brother, Nariyuki, particularly about his relationships with his female friends, as they always try to match him with them. This shows a playful and observant side to her character, as she takes an active interest in her brother's social life.

Her role in the story is primarily that of a family member who appears in Nariyuki's home life, providing a glimpse into his personal circumstances and responsibilities. As part of the Yuiga household, which includes her mother, father, older brother Nariyuki, older sister Mizuki, and twin brother Kazuki, Hazuki contributes to the warm and financially conscious family dynamic that drives much of Nariyuki’s motivation. Her key relationships are naturally with her family members. With her twin brother Kazuki, she shares a close bond and they often act together. With her older brother Nariyuki, she is affectionate and supportive, though also enjoys playfully interfering in his affairs. Her development throughout the series remains tied to her role as a younger sister, consistently appearing as a cheerful and supportive presence in her family’s daily life.

The etymology of her name provides additional insight. Her given name, Hazuki, is the traditional name for the month of August, meaning "month of leaves". This name can be broken down into the characters for "leaf" (ha) and "moon" (tsuki/zuki). Her family name, Yuiga, means "solitary" (唯我). No specific notable abilities are highlighted for her character beyond those typical of a child her age.