Completely stolen from Aestas
I thought it was an excellent idea to have my headcanon for Yoruichi in one place. For castmates' reference as well as for myself, since we currently have a couple of people who would have fair to significant amounts of shared knowledge with her. Will be updated as necessary.
--As Kisuke came to live at her house when they were both about 3 years old, she really doesn't remember not knowing him.
--Yoruichi was the target of an assassination attempt at age 4. The attacker was intercepted and captured by the house guards before getting near her, but she heard and saw enough to determine that a "Sassin"--possibly some sort of giant bug-monster--had gotten into her room while she was out playing. While she never saw the assassin, her child's imagination had plenty of fodder, and she had nightmares for months afterwards.
--She regularly beat on Kisuke for being stupid, although she eventually learned to do it when no one was watching to avoid getting in trouble.
--The first time she visited the Shiba, she was so impressed by their fireworks, she demanded to be adopted into their clan. Later, she and Kisuke tried to make their own using dirt and cooking ashes.
--She's been training in martial arts almost since she could walk; her first weapon was a small war fan.
--She was constantly surrounded by minders, and always managed to give them the slip, at least for a little while.
--She was so loud and straightforward as a child that people wondered if she would ever be able to work in covert operations.
--As a teen, she had a crush on Ukitake Jyuushirou. However, he still thought of her as a little girl, and never noticed.
--Finding out she was actually training to become an assassin took some getting used to; while she now knew better, "Sassins" had been the source of her childhood fears for a brief, but very intense period, and the feeling was hard to shake.
--Hand to hand may be her specialty, but she's been trained in the use of any number of weapons. While she doesn't use them regularly, she'll occasionally practice in order to keep her skills sharp.
--She lost her virginity to an upperclassman while in the Academy, since she wanted someone old enough to know what he was doing. He was all right.
--Unohana Retsu was her definitive model for being badass, feared and feminine, all at once.
--She didn't start to consider Kisuke as more than a friend until years after they both graduated, and well after he'd already realized how much she meant to him. Even so, it took her a long time to accept the shift in their relationship.
--The first time she had sex with a woman was the best sex she'd ever had up till that point.
--While they were in exile, Kisuke and Yoruichi took the occasional month or so off to travel the world. India, Italy and Spain remain her favorite places to visit; the food in Spain nearly made her cry with joy.
--Kisuke is very much her anchor in exile, and her wandering would take much more out of her if she didn't have him and Tessai to return to.
--As the expectation of marriage was constantly held over her head, the idea of it makes her uncomfortable.
--She assumes she'd make a terrible mother. (She'd be all right, if unconventional and surprisingly strict.)
--Soifon's rage at their reunion took her off guard because she doesn't quite realize how attached people get to her.
--She still feels guilty about how much her leaving hurt Soifon, and how much she changed in response. She doesn't like seeing someone she loves refuse to allow themselves to be happy.
--However, even knowing the effect it would have on her, she still would have left Soifon in Soul Society when she went into exile. Although, given the chance, she would have made the effort to say goodbye somehow.
--Two of the things she misses most on the Thor are sunshine and breezes; she often used to take naps in a handy sunbeam back on Earth.
--She will say that she can't cook, but the truth is, as she never had any need, she never bothered to try.
--She loves the hot springs (or hot tubs, whichever is handy).
--She doesn't drink often, but when she does, she prefers plum wine.
--She likes to dance, but rarely gets the opportunity.
--She HATES the cold, and has little shame about crowding someone for their body heat.
--Her favorite colors are orange and dark violet.
--She is an occasional marijuana smoker, but waits until she's guaranteed a night where she can just laze about.
--In her opinion, sparring can be (and has been) foreplay.
--Her favorite candy is caramel. Her favorite cake is butter mochi. She prefers tea over coffee, only drinking the latter when it has enough cream and sugar to make it taste like candy.
--She likes foods that are both sweet and spicy.
--Tends to listen to chill music. Likes certain types of Brazilian and Latin or Middle Eastern fusion, as well as some classic blues-rock (along the lines of Jimi Hendrix and Janis Joplin). Kisuke can keep his Beatles--the guitar in "Hey Joe" just might be the sexiest piece of music she's ever heard.