Kyo first met Kagura when he was very young, before his mother died. Kagura finds him alone in a playground, drawing fried eggs in the sand. Kyo tries to run away because his mother will get upset about him talking to other people, but Kagura tells him she's the boar so it's okay. She notices that he's all alone and asks if he has any friends, what else he likes, if he likes TV… Kyo says his mother won't allow him to watch tv or else she'll get angry. After a bit of a pause, Kagura asks Kyo if he'd like to play with her. Kyo looks up with such an adorable, hopeful face and Kagura tells him that she'll stay by his side. Kyo is so happy!
The two would often play together. One day, however, Kagura decides she wants to try on Kyo's pretty bracelet. He's very reluctant but she forces it off and he transforms into the demon cat. Kagura is absolutely horrified; she screams and runs away. After this, Kyo's mother refuses to let him out of the house.
We don't know too much about the rest of their childhood but we do know that when Kyo goes away with Kazuma for four months to train in the mountains, she has no idea where he is. When he returns to live at Shigure's house, she appears not too long after and is her usual demure self, asking why Kyo hadn't called. Then she suddenly starts swinging Kyo around and beating him up, yelling about how worried she was about him (she has a funny way of showing it).
It goes on like this for a while until she calms down and explains to Tohru that she and Kyo will be married in the future. Kyo says that promise was made when he was a child and also because Kagura had threatened him. Kagura is the one that demonstrates to Tohru that, as one of the cursed, she can freely embrace Kyo while any other female cannot. She turns her attention to Kyo, begging him to tell her if she likes him or not. She boasts that she loves him more than anything, even when he turns into his "true form." Kyo quickly becomes very serious and asks her to stop talking. (Needless to say, Kagura doesn't take kindly to Kyo telling her what to do and reacts violently once again. xD;)
Kagura decides to spend the night and sleeps in Shigure's office. She tells Shigure that she wishes she could start living there as well because she doesn't feel comfortable with Kyo living under the same roof as another girl. Shigure tells her that she should get the jist of how life is there by the morning and tells her not to leave the room. The following morning, Kagura tells Kyo to be well until she visits again and Kyo tells her that as long as she doesn't visit, he'll be well. Kagura becomes overdramatic once again, telling Kyo she won't give him a goodbye kiss and runs out the door -- straight into the newspaper boy. She transforms into a boar, thus revealing her cursed form to Tohru. Tohru tells her she understands why she loves Kyo so much because he has so many good traits and Kagura, misunderstanding, calls Kyo a two-timer and takes her anger out on him (again).
Unlucky for Kyo, Kagura next pops up to visit him at school, the day before Valentine's Day. All day, Kyo is visibly upset. We don't really understand why he's so put off by Valentine's Day until we see Kagura waiting for him. IT SUDDENLY MAKES SENSE. Kyo tries desperately to make a run for it but Kagura relentlessly chases after him. She wants to know if Kyo will spend the whole of Valentine's Day with her for a date. Kyo flat out rejects her. Kagura cries for a bit until she snaps out of her mood, sneakily suggesting that they could go on a double date with Yuki and Tohru. Of course, since Tohru is involved and looks so absolutely happy at the prospect of going on her first date, Kyo can't refuse and tells Kagura to do what she pleases. Before she leaves for the night, Kagura says that Hatsuharu has told her that Kyo's relationship with Yuki has improved and that she hopes the two of them will become good friends.
The next day, Kyo reluctantly goes out with Kagura, Tohru and Yuki. They go see a movie together -- which Kyo absolutely doesn't like -- before going back to Shigure's so that Tohru can make a home-cooked dinner. At least Kagura is becoming friends with Tohru~
The boar's next appearance is at Shigure's, just as Kyo returns home from school. When he opens the door, she's standing there waiting for him…. and he immediately slams the door shut on her. Kagura punches her way through the door, like the famous scene from The Shining and asks why Kyo doesn't want to see her. Scary!! Shigure suggests that the two go on a date to get groceries for dinner. Kagura readily drags a very unwilling Kyo to the store where she asks him if he plans on telling Tohru about "it." Kyo becomes serious, telling her to butt out of his business. After he thinks about it for a moment, he asks Kagura why she bothers to care about him, since people usually go out of their way to avoid the cat. Kagura coyly tells him it's a secret and asks if they can hold hands on the way home. Kyo doesn't want to and Kagura makes a big scene so he reluctantly grabs onto her hand as they walk home. Kagura sadly reflects on how it used to be Kyo who would ask to hold hands, back when they were chlidren.
As they walk home and Kyo's had enough of holding hands, they both see that Kazuma has returned. Shigure invites Kazuma in and both he and Kagura decide to stay the night. Kagura probably has an idea of what Kazuma's reasons for staying are: that he wants to remove Kyo's bracelet and expose his true form to Tohru and see how she will react. Kagura watches silently from an upstairs window and sees Tohru chase after him and later bring him back, cradling him as a cat in her arms. When Tohru comes up to the room, she pretends to be asleep already.
Next morning, when Tohru awakes, Kagura is already gone and doesn't reappear until several days later, when she shows up to drag Kyo off to Kazuma's dojo for practice. She seems to be in her usual self, as if nothing had happened.
Much later, after Kyo's school trip, Kagura approaches him at the dojo. As she goes about her usual antics, Kyo gently places a hand on her head and says they need to talk. This catches Kagura off guard, because she has a suspcion about what it is he wants to talk about… so she makes him go on a date with her, otherwise she won't listen to what he has to say. Kyo agrees.
When they go out together, Kagura says that she wants to talk to him also. She tells him that when she was a child, she was really unhappy to be born as one of the zodiac and blamed herself for all of the fighting that went on between her parents. She admits that she hated herself until she came across Kyo the first time, alone in the playground. It was then that she realised that Kyo's life, as the cat, was even worse than hers; she wasn't pitied or alienated like he was. She began to hang around him to make herself feel better and admits to Kyo that she had always looked down on him. She goes on to say she still feels guilty for having run away when she saw his true form and has always wished that she could have accepted him. She thought that maybe if she could have feelings for Kyo and get him to like her in return, then the version of her that didn't fully accept him would be forgotten. She then apologises to Kyo for being so selfish.
Kyo firmly tells Kagura that he will never love her but despite what her motives may have been, he was very happy that she played with him as a child. When he sincerely thanks her for it, Kagura breaks down crying as she realises that her feelings for him have become real. Kyo hugs her and stays with her until she stops crying.
At this point, Kagura stops hanging around Kyo as much but when Tohru comes to visit Rin at Kazuma's house, Kagura overhears Tohru telling Rin that the most important person in the world to her is Kyo. Kagura bursts through and emotionally strikes Tohru across the face, telling her that she has to say those things to the actual person.
Kyo and Kagura don't see much of each other (that we know of… maybe at martial arts practices) until the final banquet at the end of the series. Kyo sheepishly says hi and Kagura responds coldly… before grabbing onto him like her usual energetic self while Momiji takes a photo saying that being fickle is bad! Kagura joins him and Kyo is left with his jaw hanging open, wondering if they were accomplices~ xD
I think having her heart broken and seeing how Tohru accepts Kyo fully makes Kagura grow. If she had won over Kyo's heart, she wouldn't have learned anything at all. I think when Kagura finds someone else to be with, she will treat him much better for it.
I don't hate Kagura at all, by the way! I think she can be sweet and I like her relationship with Tohru very much. I also appreciate how she realises that she has treated Kyo wrongly and has the strength to confront him about it and apologise. I just think they would be a terrible couple. xD