After listening to Han Yao, Su Yu felt that all the questions in his mind were answered. Well, almost. The girl was possessed by the evil ghost and thus killed her brother or cousin. This girl should be the girl of the current descendants of the Lei family – Lei Ziyu who Han Yao said currently has a son.
No wonder why they migrated overseas. Experiencing a childhood trauma of being possessed and then when you came to, you found out that you have killed your brother (or cousin). It was also hard for the girl. The Lei family might have migrated overseas just for her. And this is the reason why the Lei family hid the truth of the past, even if it would be wronging the boy who died.
But, the questions left unanswered are: who is the evil ghost? And why would it want to kill the boy? Why did it choose the girl to possess? And… what is its connection to the Lei family?