Your mom and dad had a big fight once because he had cheated on her.. they ended up getting a divorce and your mom got a new boyfriend

Your mom and her boyfriend eventually got married, so hyunjin became your step brother, they both eventually moved into your home

You go to school and hyunjin bullies you horribly, one time he even started touching you inappropriately, but you didn't do anything about it because your mom seemed happier than ever with them