The origin is only due to the childish promise made in childhood.
He is her brother, she is his sister, they are one, he is the sun, she is the moon. They are always closely connected, but they can only stay together in the morning and evening. We meet, but there is no forever, only a moment. She wanted to leave, but he restricted her freedom and entangled her in her footsteps. He kept her, but pushed her away from him and gave her to the infatuated Yun'er with his own hands.
He was her childhood playmate, he was the cloud, tenderly guarding the quiet moon. The care he had given her as a child had already deteriorated, and the little she unknowingly occupied the softest corner of his heart. In his heart, her position changed from his sister to the woman he wanted to cling to for the rest of his life. And she still cherishes him and relies on his broad and warm heart, but she can't respond to his eagerness to wait.
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The idea for this article came from an RPG forum I played on. I also posted a similar article on the forum. After thinking about it for a long time, I decided to try to write it out.
P. S: My writing speed is variable, please forgive me...