Yunho asked Siwon to eat with him and have some talk.

    "Choi! You know what? I trust you! And I like you for my sister!" he started.

    "Thanks for trusting me" Siwon said and smiled.

    "Continue eating! I'll tell you some story of me and Yoona" he continued and Siwon do what he said. "I know you know, that our mother left us when we we're young. But, there is something you don't know about us. Even Yoona don't know" he started and Siwon listen carefully.

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-FLASHBACK-

    Yunho is only 7 years old at that time. When his mother left them.

    "Umma! Where are you going?" he asked.

    "I'm sorry Yunho but, I have to go now! Take care of your little sister okay?" his mother said and hugged him. Yunho hold her mother's hand tightly. To prevent her from leaving. But, his father took him and let her mother leave. He cried so hard and promise something to himself. "Umma! I promise I will take care of  Yoona and I promise I will....." his father asked him to go inside the house.

    He went to Yoona's room and sat beside her. He stared at sleeping Yoona's face. "Yoona. I promise I will protect you from anything. I will always make sure you are happy. Yoona... I will be a good bother and a mother to you.. I promise that." he thought to himself and cried quietly.