It was the book, How Can I Not Be Tempted? Ning Suyi and Jing Chi had been friends for generations and were not biological siblings. However, Ning Suyi always treated herself as an elder sister and kept calling her younger brother. On the other hand, Jing Chi missed Ning Suyi and wanted to be her boyfriend. They got together later on, but Ning Suyi always felt guilty and did not like to be called sister. On the other hand, Jing Chi liked this title and would always revert to his old ways. Big Sister."