Hankyung + the girl were a couple, Shiwon was a criminal who took the girl as a hostage. Hankyung was the cop who was trying to stop Shiwon, he got shot, shiwon got away. Shiwon later had to have a heart transplant, the heart he got was Hankyung's. Once he had the heart, he get getting memories/flashbacks of the girl from hankyungs point of view + then he finally figured out what happened through his hospital file, the locket, and seeing the girl.
