Ai Yori Aoshi/WMG

Miyabi lived in/grew up in abject poverty before being employed by the Sakurabas.

 * It would certainly explain her extreme fear of cockroaches and other bugs, her desire for "a beautiful atmosphere", and her fanatical devotion to her duties. Perhaps she was a menial in one of the Sakuraba stores, and somehow impressed Mrs. Sakuraba, who needed someone to help raise and teach the baby she was carrying.
 * It could also explain why, in the epilogue to the manga, Miyabi admits to Tina that . While it's entirely possible that there are mundane reasons for this, the possibility that she's from a considerably more impoverished background may also explain it.
 * Partially Jossed. She couldn't have been working for the Sakuraba company, since she was either a teen or very close to it when she was employed to care for Aoi.
 * Her backstory is that her parents worked for the Sakurabas for years before they got killed in a car accident. Aoi's mother took Miyabi in, and Miyabi dedicated herself to Aoi to repay Aoi's mother for taking care of her. It doesn't necessarily preclude her being poor or in otherwise filthy conditions before then, though, although the opposite could be true- that she's never seen cockroaches and the like much before.

Miyabi likes Kaoru that way.

 * You can't help but notice how she tends to overreact to physical contact with him by the standard Tsundere defense mechanism and/or blushing, such as when he catches her by the arm after she trips on the lamp, or when she lands on him after rescuing Uzume from the clock. This doesn't preclude theories about her liking Aoi as well.
 * Glad I'm not the only one who thought this way. While evidence in the manga is slim to none for this theory, in the anime, especially after Kaoru braved the then decrepit summer home's office area, it struck me that she felt like she may have found a Knight in Shining Armor. His gentle and caring demeanor toward everyone in the home and his near limitless patience perhaps only cemented this view of him in Miyabi's mind. Watching her around others and then around Kaoru shows a marked softening of her disposition.
 * Must... resist... writing... fanfiction about Miyabi and Kaoru...