They were two people born in the 1980s living together in a small city in Tianning. The little girl's secret love began and gradually progressed. But Dong Tianhao turned into Zheng Yan after leaving, and Yatou's Tian'er brother turned into Brother Shitou.
Cosmos is the true heart of a girl. See the true heart of a girl from the perspective of a steady man like Zheng Yan.