Friendly Rivalry — Ending Explained

The Father's Death Scandal: Woo Seul-gi's father did not commit suicide unprompted. He was blackmailed and manipulated by Dr. Yoo Tae-joon (Jae-yi’s father), who ran an illegal ring leaking CSAT exam questions to elite students.

Yoo Je-na's Tragedy: Jae-yi’s late sister, Je-na, was driven to extreme distress due to Tae-joon’s psychological abuse and manipulation, fueling Jae-yi’s hidden quest to ruin her father.

The "Vitamin" Revelation: The series leads viewers to suspect Jae-yi is poisoning Seul-gi with dangerous study drugs. In reality, Jae-yi swapped Seul-gi’s pills with harmless vitamins, keeping her safe while maintaining the illusion of compliance before her father.

The Finale & Ending: In Episodes 15–16, Seul-gi and Jae-yi dismantle Tae-joon’s crimes. Jae-yi stages a dramatic water scene with Je-na’s ashes and disappears, leading authorities and her father to search for her endlessly. The series closes on an open note: Seul-gi tracks down Jae-yi’s hidden location, reuniting with her away from the corrupt world of Chaehwa High.

• The Rebirth & Freedom Reading: Jae-yi’s dive into the water with Je-na’s ashes in the final episodes is interpreted as a symbolic suicide of her old identity. By letting the world believe she disappeared, Jae-yi frees herself from her father’s shadow to start an unburdened life.
• The Unconventional Love Story: Rather than a pure thriller, critics and fans interpret the show as a complex romance where Jae-yi assumes the role of an antagonist to protect Seul-gi from her father's criminal network.
• Systemic Indictment: Viewers note that while individual villains like Dr. Yoo Tae-joon are brought down, Chaehwa High and the CSAT exam machinery remain untouched, highlighting that the system will simply produce new victims.