A drama about an old man who is lost in the memories of 1945 Hiroshima after getting an unforgettable birthday letter from his first love. During the Japanese colonial rule era, Moo Gil and Il Ae are childhood friends and each other's first love. Against their wills, both Moo Gil and Il Ae have to leave Hapcheon, South Korea, and go to Hiroshima, Japan. They are separated from each other there. Then in 2019 in South Korea, Moo Gil receives a birthday letter from his first love Il Ae.
Han Woo-Jung (Seo Hae-Won) has a bright personality. She is betrayed by her best friend Shin Hwa-Kyung (Oh Seung-A). Because of the betrayal, Han Woo-Jung's life is ruined. Han Woo-Jung keeps pursuing her dream and never loses hope.
Kim Jae Min is a sweet husband who will do anything for his wife Lee Mi So. Mi So has a bright personality, but she learns that she is pregnant with their second child. Even with just one child, she has a hard time raising their child and working. Kim Jae Min decides to submit for a maternity leave at his work and begin to raise their child and do house chores.
