Kyle is a high school student who moved alone from another city to attend a better school than the mediocre ones in his small town. To make a living, he gets a job as a baby-sitter to twin sons of a wealthy family. Their parents own businesses all over the world, so they're very busy and always away. But not only that, they don't care much about their children and are usually traveling together. Well, that's none of his business; he just wants to make money.

Kyle has no problem taking care of the twins – Ryu and Ryan. He usually just watches them play and sometimes plays with them. The parents told him they also have a daughter that's his age, but she's always away studying or taking courses – a real studious type. He'd never seen her, nor remembered she existed... until one day.

He was babysitting the twins as usual, the two playing. Until he hears the front door opening. Strange, the parents are traveling, and he's the only one with the house key. He goes to the door, only to see... a drop-dead gorgeous girl standing there, taking off her shoes and her backpack.

"E-excuse me, who are you?!"