A Blood Pledge

Ki-ho is So-Hee's boyfriend who appears to drift away after Eun-Joo's death. His memories and flashbacks reveal a complex web of past romance and present disinterest, underscoring how relationships fracture under pressure. He ultimately moves on, signaling a fallback to ordinary life beyond the group's tragedy.

The central catalyst who initiates the suicidal pact and whose death haunts the surviving girls. Her presence lingers as a ghost and as a voice that pushes So-Hee toward accepting the burden of responsibility. She embodies the hidden rage and longing that ends in tragedy.

Ambitious and driven by grades, Yoo-jin uses social status and academic success to control her friends. She manipulates situations to maintain top standing, participating in the dangerous stunts on the roof. Her actions reflect how competitiveness can corrupt empathy.

A fragile girl haunted by an abusive father and fear, she experiences visions of Eun-Joo and becomes a target for the cycle of fear. She seeks safety with Yoo-jin but ends up in a deadly confrontation that exposes the danger of domestic violence.

A friend who becomes a casualty in the escalating tension, captured in the web of shifting alliances and betrayals. Jung-yoon's fate illustrates the fatal consequences of the group's tangled secrets and the ever-present pressure to hide truth.

Racked with guilt and depression after Eun-Joo's death, So-Hee becomes the emotional center of the story. She contends with a pregnancy that adds moral weight to her choices, and she ultimately takes responsibility for the baby and for Jeong-Eun's fate.

So-Hee's sister figure who appears in flashbacks and becomes a protective anchor in the present. Jeong-Eun's role reveals the siblings' bond and heightens the stakes of So-Hee's decision to keep or lose the unborn child.