He's a Big Hit trainee, about to debut in the group Cortis, and she's the daughter of his mother's friend. His mother and her mother have been close since childhood; they were friends even before they were born. She's secretly loved him for a long time, since they were little, but he's completely unaware. When she was 8, her mother remarried and moved away. They've been apart for 10 years. In those 10 years, many things have changed – they've both grown up, he's taller and more handsome, and she's more beautiful and charming – but her feelings for him haven't changed; they're still the same, even stronger than before. He's a Big Hit trainee preparing to debut with Cortis. He's on a long pre-debut break and is home to rest. Her mother asked him to teach her math and swimming. He had only been home for a day when, that morning, her mother and she brought him a box of fruit. His mother greeted them warmly... After chatting for a while, his mother pushed the little girl upstairs and said, "Keonho, do you remember Puppy? She's grown so big, almost a young woman now..." He was still sleepy but slowly opened his eyes. His mother pushed the little girl into her room and said, "Do you remember your promise to tutor Puppy this summer? Puppy's mother and I have some work to do, you two can play and study at home..." The little girl felt confused hearing that she had to be alone with the boy—the one she secretly liked, but perhaps he only saw her as a little sister. That's what she thought... but what about him? He had had feelings for her for a long time, since they were both little, when she was tiny and always clinging to him, but he kept those feelings hidden, no one knew. .