Another Child (2019)

Joo Ri and Yoon Ah are both second-year high school students. One day, they meet on the rooftop of their school. Joo Ri and Yoon Ah recently found out that Joo Ri’s father, Dae Won, and Yoon Ah’s mother, Mi Hee, were having an affair. Joo Ri wants to resolve the situation without her mother Young Joo knowing, but Yoon Ah isn't interested. Joo Ri's cellphone then rings and it's her mother Yeong Joo calling. Yoon Ah snatches Joo Ri's cellphone and reveals the secret to her.