Dongsi Seventh Hutong has been there since the Ming Dynasty. You live at No. 3, Chu Can lives at No. 5, and Zhou Bai lives at No. 7. The courtyard walls of the three families are right next to each other. In the summer, everyone would eat while visiting each other holding their bowls. If your mom ran out of green onions while cooking, she could just yell over the wall and get them handed to her. The three of you have played together since you were running around bottomless as toddlers. Now that you're in high school together, you still stick to each other every day. The three of you—eating at your house today, sleeping at mine tomorrow. The people in the hutong all laugh and say that the three of you kids are just like real siblings. But no one knows— During Chu Can's sophomore year of high school, you wore his school uniform jacket to the convenience store. After you came back, he folded the jacket neatly, put it at the very bottom of his wardrobe, and never wore it again. During Zhou Bai's freshman year of high school, you told him that a boy in your class was pursuing you. He froze for a second, then smiled and said, "Which bastard?" Later, that boy never appeared in front of you again. Neither of them said anything. But they both knew that the other hadn't said anything either. Until last month when someone stuffed a love letter into your desk, and Chu Can and Zhou Bai saw it at the same time. That night, the two of them sat on the rooftop of Chu Can's house for a long time. Zhou Bai spoke first: "You saw it too?" Chu Can didn't say anything. Zhou Bai smiled, a smile with a hint of bitterness: "I thought it was just me." Chu Can was silent for a long time. Then he said: "So what do we do?" Zhou Bai stood up, looking at the window of your house in the distance, where the light was on: "Nothing. Just watch over her." Chu Can also stood up, standing next to him. "We have an agreement?" Chu Can didn't answer. But he reached out and patted Zhou Bai's shoulder. That gesture spoke louder than any words. From that day on, some things quietly changed—