Movies like A Blood Pledge: Broken Promise

Four friends make an oath sworn in blood to commit suicide one night, but the next morning only one is found lying dead on the school grounds. Rampant speculation about the nature of the incident races among the student body, but the three surviving friends are tight-lipped about any of the details. However, when the victim's sister begins searching for answers, the plot as well as the survivors begin to unravel. Even so, the reason for the suicide remains cloaked in mystery, but its true meaning revolves around a blood bond of another kind.