Hanamaru Kunikida is a first-year student at Uranohoshi Girls' High School, later transferring to Numazu High School following the former's closure. She comes from a family that has run a local temple for generations, and she lives with her grandparents, which has shaped much of her upbringing.

Her background as a temple girl means she has grown up with limited exposure to modern technology, as she does not have a computer or television at home. This has fostered a deep love for reading, and she can often be found in the school library, where she serves as a library committee member, immersed in Japanese literature. Her dream is to become a writer someday. This disconnect from contemporary life makes her easily fascinated by modern gadgets and the internet, often leading her to exclaim her signature phrase, "Mirai zura!" which means "It's the future, zura!".

In terms of personality, Hanamaru, who often refers to herself as Maru, is a gentle and caring individual, though she is prone to self-deprecation. She describes herself as a chibi procrastinator who is neither cute nor interesting, and compares herself unfavorably to her more dazzling friends. Despite this quiet and sometimes insecure exterior, she possesses a playful and mischievous side, particularly in her interactions with her childhood friend, Yoshiko Tsushima. She delights in teasing Yoshiko about her fallen angel persona, often in tandem with their mutual friend Ruby Kurosawa. Another notable trait is her surprisingly large appetite; she is frequently seen eating sweets, with a particular fondness for a bread roll known as noppo bread. She speaks with the melodic lilt of the Shizuoka dialect, ending her sentences with the verbal tic zura and using the pronoun ora to refer to herself.

Initially, Hanamaru is hesitant to become a school idol. She feels she lacks the necessary physical stamina and does not see herself as fitting the glamorous image of an idol. Her motivation to join Aqours is deeply rooted in her relationships with others, especially Ruby Kurosawa. Hanamaru is fiercely protective of Ruby, her best friend. She pushes Ruby to follow her own heart and confront her older sister, Dia, about her desire to become an idol. Even after pushing Ruby forward, Hanamaru intends to remain in the background, believing her role is to support Ruby's dream from the sidelines. It is only when Ruby, inspired by the story of muse member Rin Hoshizora, returns the favor and encourages Hanamaru to believe in herself that she finally decides to join Aqours as its fifth member.

Her key relationships are central to her story. Her bond with Ruby Kurosawa is the most prominent, defined by mutual support and admiration. She is also close with Yoshiko Tsushima, having attended the same kindergarten, and she understands Yoshiko better than most, seeing past her chuunibyou delusions to the friend she has always known. As a first-year student, Hanamaru initially struggles to relate to the more mature third-year members, finding common ground with them over calmer, indoor activities during a rainy day in the second season, where she particularly connects with Kanan Matsuura.

Throughout the series, Hanamaru undergoes significant development. She transitions from a shy bookworm who hides in the corner of the library and is insecure about her physical abilities to a more confident performer on stage. She learns to value her own strengths, including her intelligence and her gentle nature, and finds a place for herself within the group. Her role in Aqours is not just as a singer, but also as a thoughtful and observant member who offers sage advice and keeps her friends grounded. Her notable abilities include being a gifted singer, a skill honed by her membership in a choir, and her voracious appetite for reading gives her a broad base of knowledge.