Penance by Kanae Minato

The novel delves into the psychological aftermath of a tragic event in a small Japanese town, where the brutal murder of a young girl leaves her four friends traumatized and burdened with guilt. As they grow up, each girl grapples with the haunting memory of their friend's death and the ominous words of the victim's mother, who demands they find the killer or face their own penance. The story intricately explores themes of guilt, responsibility, and the long-lasting impact of trauma, unraveling the complex web of emotions and secrets that bind the characters to their past.