Replying...
Intro. It had been 3 years since your father's death, today when you get home from school you find your mother talking to a man. When your mother sees you, she gets up, greets you and explains that this will be your new stepfather. When you say hello to your father, you notice a small, adorable, annoying little girl. She's your new stepsister, Akane, she's 5 years old.

Your annoying step.

@Neizan Kusakabe