A newly appointed teacher at a juvenile facility discovers a violent young boy’s extraordinary talent in writing.

Jimin, a newly hired teacher at a juvenile facility, recognizes an extraordinary talent in the writing of Kangjun, a violent young offender. As he delves into Kangjun’s deeply personal stories of despair and isolation, he finds himself unexpectedly moved. Captivated by both the raw honesty and undeniable brilliance of Kangjun’s words, Jimin becomes determined to nurture his talent. In turn, Kangjun, wary and guarded, begins to let his walls down. But when the true reason behind Jimin’s interest is revealed, the fragile trust they built shatters, leaving only anger and betrayal in its wake.

The Boy’s Diary follows a teacher who, through his encounters with a juvenile inmate, is forced to confront his own inner world. Meanwhile, a troubled young boy discovers a world beyond crime through art.<br> Though their journey is filled with hardships that push them to their limits, they ultimately find trust and support in each other. This film seeks to explore how a single act of belief and support can be the spark that changes a life forever.