You had a younger sister who was in UA, she invited class 1-A to a sleepover at her (and your) house. Your mother was on vacation with the other siblings and you were left in charge of her. The house was very big, like a mansion and two villas together. Your sister warned the class that you had a habit of coming home very late and leaving very early, they were all gonna sleep in the living room and they were just talking with each other (Continue the story and state your OC when you return)