Oono is a first year student of Fujigaya introduced at the beginning of Akira and Fumi's second year of high school. She is an energetic and blunt girl, and she considers it a personality flaw that she speaks her mind clearly and ends up hurting people's feelings unintentionally many times because of it. She is extremely brave and very self-confident; she quickly becomes friends with older students from both Fujigaya and Matsuoka. She even calls Yamashina-sensei by her nickname "Hina-chan" in school though she is corrected and told to address her teachers appropriately at school. Haruka initially joins Fujigaya outside of the school's elevator system, meaning, like Akira, she did not attend the elementary or middle schools and wrote an exam to gain entry. This causes her and Akira to quickly become friends as they are both "outsiders" as compared to the other girls there who have known each other for much longer. Haruka's initial reason for attending Fujigaya was to meet Sugimoto Yasuko. A year earlier, she attended the Fujigaya drama festival with her older sister, Orie. Yasuko's performance as Heathcliff moved and inspired Haruka to attend the academy. She was disheartened to learn that not only has Yasuko graduated but she even left the country. She felt even more foolish when she realises that Yasuko was not even a student of Fujigaya but of Matsuoka (implying that Haruka would have attended Matsuoka if only she knew). She joins the Drama Club and manages to recruit Ueda Ryouko into acting in the school's new play. She becomes much closer with Fumi who she meets through Akira. She and Fumi, though having a rocky start, eventually become good friends. Haruka even invites the older girl to her house. There, she confesses a secret that had been bothering her for a long time: Haruka found a love letter sent from Hinako to her sister Orie. She believes her sister to be a lesbian and has a hard time accepting it and does not know how to deal with it. She asks for Fumi's advice unwittingly, not knowing that Fumi herself is gay. After that, she notices that she put Fumi in an awkward position and thinks that she has crossed a boundary in their confidence in one another. She tries to make right with Fumi after believing that she offended her or scared her off, showing that she is braver than Akira (who did not want to face Fumi around this time as well due to a certain event that drives a wedge between the best friends). Haruka eventually speaks to Fumi and realises, by extension, that she has to face and accept her sister's sexuality.