"Birthday Letter" is a story about an old man named Kim Mu Gil who received a birthday card made by his unforgettable first love and returns to his memories from Hiroshima in 1945.

It shed new light on the painful lives of the youth during that time that experienced the Japanese occupation of Korea, Korea's liberation and the Korean War. Jun So Min also known as Kim Je Yeon is a webtoon artist in the story and the granddaughter of Kim Mu Gil.

During the first teaser, Kim Mu Gil endures forced labor in Hiroshima during the time of Japan's occupation in Korea. A woman narrates, "Whatever happens, make sure to return alive." Though he promises this to come back the screen suddenly turns into a white one. The man recites, "It is a bomb, it is a bomb." And repeatedly calls for his first love Yeo Il Ae also shouted, "Mu Gil".

Into the second teaser of the story, it features Jun So Min who will play the role of Kim Jae Yeon who retrieves a letter from the mailbox that was addressed to her grandfather. She asked her grandfather, "Do you know someone named Yeo Il Ae?" And later with questions "You want me to go?" As she asked for Yeo Il Ae the video flashes back during the year 1945.

After that Kim Mu Gil finds Yeo Il Ae and he happily commented, "Do You know how long I have been searching for you?" then Yeo Il Ae responded to him, "Don't come back." Though he intends to reunite with her, the screen once again turned into white before Kim Mu Gil finally said, "I will come back every day."

The drama "Birthday Letter" is written by Bae Soo Young and Jun So Min who starred in the writer's latest project entitled "Review Notebook of My Embarrassing Days" through their past connection Jun So Min reportedly agreed to star in the "Birthday Letter" as soon as he received the final script. Through their past connection Jun So Min reportedly agreed to star in the

"Birthday Letter" as soon as he received the final script. The touching and emotional story of "Birthday Letter" airs this September 11, 2019, at 10:00 PM KST.