There really weren't any unspeakable secrets between them; they simply had both attended the same school.
The assistant director was Xiao Yu's senior at school, and with this relationship, he would take care of this junior sister on the set.
Furthermore, Director Xu was always very strict with actors, having made even many famous actors cry. As for a newcomer with little fame like Xiao Yu, he would scold her even more harshly, and when he lost his temper, he might even throw things around.
Though the position of assistant director sounds prestigious, in reality, it involves doing all sorts of miscellaneous tasks, including providing psychological guidance to young actors when they have mental issues.
As time went by, Xiao Yu became increasingly dependent on him and subconsciously sought help from her senior whenever she encountered difficulties.