Ryu is a talented young writer who has been in a relationship with Pin since high school. Despite their love, Ryu's fate leads to the tragic loss of his girlfriend in a car accident.
Overwhelmed by guilt and remorse, Ryu withdraws from society and turns to alcohol for comfort. However, as he slowly recovers, he meets Arm, the grandson of the company where Ryu works. Arm's kindness and understanding soon bring warmth back into Ryu's life.
As they spend more time together, Ryu learns that Arm has a secret: she is actually Ryu's biological sister. Their revelation brings them closer than ever before, but when Ryu discovers he has cancer and may not have much time left, he realizes that their bond is too strong to let go.
Arm decides to take care of Ryu and the two decide to live together. They face many challenges, but their love and support keep them going.
However, their happiness is short-lived. When Arm and Ryu discover the truth about something that tears them apart, Ryu disappears from Arm's life. Arm searches tirelessly for Ryu, but without success. Until finally, she receives a box that contains all the answers to their past.
