Chaerin and Dara were together in high school and best friends. Dara was the most 4D and innocent person that Chaerin knew.

They lose contact when Chaerin goes to college and Dara moves in with her boyfriend.

A few years later, Chaerin and Dara have an accidental meeting...a meeting which shocks Chaerin beyond belief. She just knows one thing; she didn't stop her best friend when she was doing the wrong thing before...she won't repeat the mistake again.