Yeo Jin-goo died on his birthday trying to save a friend.
On the first episode of the SBS drama "Reunited Worlds", Seong Hae-seong (Yeo Jin-goo) was in 11th grade when he took graduation pictures with Jeong Jeong-won (Chaeyeon).
This picture became his funeral picture. Seong Hae-seong narrated, "I died at the age of 19".
12 years later, Jeong Jeong-won (Lee Yeon-hee) was a thirty-one year old grown up. She visited Seong Hae-seong's memorial and saw a strange white smoke in the sky. At the same time, Seong Hae-seong woke up on the school roof and also saw the strange smoke.