5-year-old On-yoo has been waiting for a heart transplant for 2 years due to a heart condition since birth. He was finally able to live a new life after receiving a donated heart from a child who passed away in an accident. On-yoo is now growing up healthy and playing with his friends. However, behind his happiness lies the sacrifice of an unknown 'angel'. On-yoo's mother wants to express her gratitude to the donor family someday. However, direct contact between recipients and donors is currently impossible due to regulations related to organ transplantation.
