Kyoko Yukino very close to being the best student of the school, and that's why she is competing for the SOY title (Student Of the Year), which would give her the opportunity of studing in a prestigious University. However, her life is not as good as it seems, she doesn't have many friends and when she crosses paths with certaing guy as he is having fun with his girlfriend and he proposes to be friends to her, she can't quite forget the incident.
Her mother works for a company called "Nippon House Keeping," which, as the name says, sends employers to clean and keep houses. And Kyoko doesn't have any specially good memory of her growing up, with her mother always caring about her work, friends and specially certain "Tamaki" from the household where she's been working since young--and not for her.

On the next day at school, Kyoko receives a shock: there is somebody else competing for the SOY! As if things weren't bad enough for her, her mother hurts her ankle and so tells Kyoko to go make her job.
Kyoko doesn't want to, but when her mother begs her, she is so suprised (it's the first time her mother ever asked something like this--almost pleading) that she accepts. The deal is supposed to be for that same day, so Kyoko goes to the house of the Renjou family, knowing that the same Renjou Tamaki (who is supposed to be the head of the family) is her new competition for the SOY and the guy she's been jealous of for a long time.

When she arrives at the house, the first person she encounters is a young, blonde guy. She is very shocked that this is Tamaki, and even more when the boy starts to treat her like trash. But just when she is about to explode, the guy faints at her feet!
Kyoko doesn't know what to do, and in that moment the same guy she encountered before in the school enters the house. She thinks (even in a bigger shock) that this has to be Tamaki, since he's obviously older than the blonde guy. But the man corrects her and tells her his name is Mito and that the blonde boy is his brother Shizuka. Tamaki seems to be their older brother.
Mito helps taking Shizuka upstairs, and he is impressed when he sees Kyoko all worried and taking care of Shizuka's fever. Later in the night, when she is making dinner for them, Tamaki finally appears. Kyoko can't take her eyes off this tall, black haired, hiper-cool looking guy. So much that she forgets the dinner and it burns, to Mito's disgust.
After dinner, Tamaki goes out with Kyoko when she has to go, but after discovering what a nice person he is, she runs away very confused because she likes him, while she is supposed to hate him. But problems have only started for Kyoko, because when she arrives at the hospital to visit her mama, she tells her Kyoko has to go take care of the Renjou house for the whole time her mother is inhabilited! Kyoko's mother doesn't care very much about Kyoko's complains that she has to study a lot for the SOY (wasn't her being the best what her mother seemed to want, anyway?), and Kyoko sees herself already like an old-fashioned maid. ^^

Next day at school Tamaki visits Kyoko in her class, but she is not very happy and still glooming about the fact that she has to go take care of them and their house so she walks away. Tamaki tries to stop her and they both end in the teachers' longue, where Tamaki learns that Kyoko is running for the SOY too.
Kyoko goes away from the room outraged at some words Tamaki's sponsoring teacher has said about her, and ends up in the sports' fields, where she sees Mito playing soccer and learns that he is the star of the team and an ace.
Later on she encounters Tamaki while she is shopping in the supermarket, and he tries to cheer her up, something she doesn't like because it makes her like him even more. Back in home while she is making dinner, Mito returns home with a very beautiful woman... who says is the guy's mother.