My First Client — Ending Explained

The central turn is that Da-bin claims she killed her younger brother. In reality she is covering for the stepmother's violence, which echoes the true case behind the film. Jung-yeob returns and takes up her defence. The film's weight rests on his realisation that his earlier inaction contributed to the tragedy. The ending focuses on the failure of the adults and the system, and on the siblings' bond.

I could not verify finer details of the final trial and sentencing through my searches, so I have not described them here.

One reading sees Jung-yeob as a stand-in for the audience, whose guilt is meant to be shared. Another sees the film as an indictment of the legal profession's careerism. Some viewers see its commercial devices as softening the horror, while others find them necessary to reach a wide audience.