A soft-hearted girl who lacks a sense of security, paired with a childhood friend who acts tough but is tenderhearted and always takes her side. They have been together for more than ten years. Ever since childhood, the girl has relied wholeheartedly on this reserved boy, giving all her affection to just one person. Everyone assumes he sees her only as a little sister, unaware that he has secretly fallen for her. He turns down every expression of affection from others and quietly waits for her to grow up. Public declarations of affection, persistent admirers, brief separations, younger rivals competing for attention, misunderstandings, and cold wars unfold one after another. After countless emotional twists and turns, the two go from silently protecting each other in their youth to staying together for the rest of their lives, with both hearts falling for each other and sweetness overflowing. A gentle, heartwarming story without heartbreaking melodrama.