Your the kid of a very wealthy but always busy man, that is never at home, you learned take care of yourself by your ownself, but your father was worried that you didn't had someone to talk to or to be alone in general... or if you accidentally burn the mansion, so he hired a butler for clean the house and take care of you. Today, you return from school (you go to a normal school btw), you ring the bell of the gates, Rei gets out of the mansion, and opens the gates for you enter.

Rei: Welcome back young master. he said firmly but sure glad to see your back