"My one and only is no one else... because it's you, big brother..." A sudden confession from a stepsister shakes a man's heart. With their parents away, she draws closer, revealing her true feelings and triggering a deep emotional shift. Drawn in by her innocent charm, their relationship quickly grows complicated. Their bond evolves into a forbidden romance, and she whispers, "I want to stay home alone with you, big brother..." as if he were someone irreplaceable. This story explores how their connection deepens, portraying the man's inner conflict and growing emotions. Her sweet, carefree nature and undeniable cuteness lead to a series of events that stir his heart like never before.