Spoiler (highlight to view)
Usui is actually an illegitimate son of a wealthy family in England (shock?) which, means he's not full Japanese. In fact, Usui's grandmother, who is Japanese, married his grandfather, who is English, and the two gave birth to a half Japanese, half English daughter. The daughter is Usui's mother. She got married to someone (unknown) and they had a son but then during her trip to Japan, Usui's mother met Usui's father and ta-dah! However, due to the fact that he is an illegitimate child, Usui's grandfather made Usui's existence unknown to the family in England. At a certain point, Usui's grandfather sent Usui to Japan where he will be under the care of Usui's mother's cousin (on the grandmother's side). Usui was home schooled for a while and then he requested to be admitted into high school (Seika). Basically, instead of being an heir to a company, he is an illegitimate child whose existence is a secret. His family is only going to support him till he can enter the labor force.
*Note: Usui's mother died giving birth to him.
At least that's what has been revealed (by the 47th Chapter).