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"I swear I will protect your love!"
Aoi's appointed guardian and caretaker, she spent most of her life looking after Aoi and helping in her uprising. She's also very active in the running of the Sakuraba Department Store. She's generally very strict and enforces the rules of the Sakuraba summer house as the manager. We first see her in Kaoru's apartment. When Aoi tried to wash Kaoru's back, he tried to leap out of the tub and cover himself. Instead, he slipped and fell on her in a very provacative style. Aoi screams and Miyabi bursts through the door, throws Kaoru across the room and begins to stomp on him until Aoi stops her. She tries to take Aoi back to the Sakuraba, but Aoi runs away from her to stay wtih Kaoru. Despite her initial dislikes of Kaoru and all of his friends, she learns to accept him because of the feelings that Aoi and Kaoru have for each other. She is somewhat humbled in the episode where Tina is introduced courtesy of losing in a drinking game with her. She's also very fond of breaking watermelons in the summer. She is fiercely protective of Aoi's feelings and reprimands Kaoru sharply when he stays out all night with Tina and leaves Aoi waiting up with his dinner. As time goes by and she begins to trust him more, she looks the other way when they try to be alone and even goes so far as to help them find places to be alone later in the series.
Although the impression is given that she is a tough-as-nails workaholic, she shows various signs of being a very deeply compassionate person. When the pet ferret was in danger of dying from being crushed by a gigantic heirloom pendulum clock, for all her initial dislike of the animal she raced to find a crowbar which she then used to free the ferret, which later became more attached to her than to Tina. Aoi later explains that the ferret could sense the kindheartedness within Miyabi's samurai-like demeanor.
In the manga, it's revealed that her parents worked for the Sakuraba family before they passed away from an accident. Aoi's mother then took in the orphaned Miyabi, who then was tasked with caring for Aoi. She has great respect for Aoi, and shows this by adding the honorific "-sama" after her name. After accepting Kaoru, she adds the honorific "-dono" after his name. The first time the Sakuraba try to steal Aoi back, Miyabi fetches Kaoru in the dead of night to take him to her at the inn. She confesses that she has hated Kaoru since before she knew him because he was always the center of Aoi's world. No matter what Miyabi did, Aoi only ever talked about Kaoru-sama. When the couple first moved into the summer home, we see a seen of Miyabi in the bath, heartbroken that she could never make Aoi-sama smile the way Kaoru does and reprimanding herself for her harsh treatment of Aoi.
Her given name means "refinement", which befits her role of training Aoi to be a good wife.
In the final chapter, which happens four years after Tina has returned to the United States, Miyabi has been adopted by the Sakurabas. She's also a manager of a department store owned by the Sakurabas.