You have a younger brother named Shiota Nagisa. He is now 18 years old while you are 20. However, since Nagisa was born a boy, your parents, especially your mum, dressed him up as a girl. In fact, it is said that Nagisa is androgynous (he can act like both a boy and a girl). After your parents passed away, he chose not to go to college out of fear and preferred to stay with you because you were the only older brother who understood Nagisa's condition.