Aoi Hyūga (日向 葵 Hyūga Aoi) is Natsume's cheerful younger sister, appearing mainly in the manga. Aoi tells Ruka that her brother doesn't smile often so she has to smile for him, and so she is usually seen with a cheerful smile on her face, even when shocked or surprised, much like Koko. She originally possessed a Fire Alice like her brother, but it eventually disappeared.
Aoi was, at one point, referred to as "Yuki Aoi" by Persona, possibly so that Natsume could not find her as easily.
Aoi has black hair and red eyes like her mother, Kaoru. She somewhat resembles her mother, but not as much as Natsume.
When shown in flashbacks Aoi was always seen as a cheerful, cute young girl; the exact opposite of her brother, Natsume who gave others the cold shoulder. Aoi stated to Ruka that her constant smile was for her brother who would not smile. Years later, while imprisoned deep within Hana Hime Den Aoi started to not smile anymore and her life was a delusion in thinking that Persona was her "brother". After regaining her memories Aoi is seen smiling again and is happy because Natsume has people who care for him.
Aoi and her family moved to a village where Ruka Nogi lived. She was introduced to Ruka by her brother, Natsume and grew to like him and call him by his nickname. The day Ruka slept over, Aoi found a red stone that she kept, because the color reminded her of her brother. The stone was left by Persona and was meant for Natsume. While sleeping the stone disappeared in Aoi's hand. The next morning she did not go to school, because of a high fever and only talked about the missing stone. Natsume left having Ruka watch her. Her fire alice then went out of control and burning the house and quickly pasting down to the village. The stone was later found out to be a experimental amplification stone that was unstable. At the hospital, Natsume took the blame for this and Aoi lost her eyesight and memories. Persona then appears in Aoi's hospital room and tells her that he is her brother. She is then taken to the academy to heal her eyes, but is used to keep Natsume obedient.
Mikan Sakura finds Aoi in a prison in Hana Hime's basement. Mikan then asks if Aoi is a student and the two bond easily, because of their similar personality. Mikan figures out that she is blind when Aoi touches her face saying that she is also cute. Aoi tells Mikan that she is not a student, but here to cure her eyes. She then questions if she should tell Persona about Mikan, because that would make Persona angry for letting anyone here. When Mikan asks why she is here, Aoi tells her that she is not an alice and Persona has kept her here, because she has no where to go and that the academy does not allow non-alices, indicating that Aoi does not remember anything about her past. Aoi speaks to Mikan about Persona's past and Mikan learns that Aoi does not smile like she used to. Mikan soon leaves, telling Aoi that she should leave this place and go to her important person (Natsume). When Mikan leaves someone opens the prison for her and Aoi escapes.
She appears where everyone else is and does not know who Natsume is when he comes near her. Natsume protects her with his flames and speaks to her that he will protect her this time. This causes Aoi to remember Natsume as her brother. As Persona inflicts his alice on Mikan, Aoi tries to convince Persona, who thinks she is betraying him, to stop. This makes him attempt to use his alice on her, but is stopped by Mikan.
Aoi is with everyone when they take Mikan to the hospital and there when Natsume says that he will take Aoi and leave the academy, who is told that the two would get captured and taken back. Since Aoi has no alice everyone spreads newspapers about her, attempting to get her out of the academy. Aoi then with Natsume reveals herself to everyone on the rooftop. With this Aoi and everyone is at the front gate saying goodbye to her. Where it is learned that she has regained her eyesight and that she asked Natsume to return home with her, but he refused. She tells them to take care of her brother and that she will be waiting for him. At the gate everyone says goodbye to her. When her father arrives both are hugged and she is taken home. Aoi is happy that so many people understand her brother.
Aoi had a Fire Alice, like her brother and father. However, it was an Intermittent Alice, so when the stone made Aoi's alice go out of control and burn her entire town down, it disappeared. Nonetheless, she continued to stay at the Academy for some time, acting as the only non-Alice person there.
- The kanji reading for Aoi is "hollyhocks" and is also used in "mallow", and "wild ginger", and not the kanji for "blue."
- Aoi does, in fact, appear in the anime, during the fire at the Academy, in Episode 11. However only her back is shown and her only line is 'Save me... and murder'