Thirteen-year-old Tomoya Mizuhara leads a perfectly normal life until his father suddenly decides to get remarried. Overnight, Tomoya finds himself saddled with an incredibly enthusiastic seventeen-year-old stepsister named Ichika. Unfortunately for him, Ichika is far from normal, and her intense, smothering affection for her new little brother borders on terrifying. To make matters worse, Tomoya must also navigate Ichika's eccentric circle of friends, including a ruthless sadist named Ruri and an attractive, airheaded foreigner named Marina, leading to a chaotic daily routine.
