It was when Mu Yan was in fourth grade that she remembered the big change that Tang Bei had made towards her. Tang Bei, who was in sixth grade that year, except for the occasional exchange of words with Meng Shuke, who was in the same grade, was almost isolated from all his friends, feeling depressed, as if he had sealed himself in a cold world.
At that time, they had not moved yet and lived on the fifth floor of the same building. That was when Mu Yan, who was in fourth grade, squatted at the door of her house when she came home from school, waiting for her parents to open the door after get off work. Through the stair railing, she saw Tang Bei coming up from the fourth floor. She excitedly called out his nickname as before, "Brother Beta~Brother Beta~" However, except for Tang Bei's indifferent glance, Mu Yan did not get any response - she watched him open the door and close the door silently. Then, she was left alone, carrying her schoolbag and staying alone in the space on the fifth floor.
What is the reason that makes Tang Bei gradually stay away from Mu Yan? When they grow up, will they drift further apart or get closer step by step?