Ryu is a skilled young writer who has a girlfriend, Pin, who he's dated since high school. They love each other and plan to marry. But perhaps because of Ryu's fate, he loses her forever in a car accident.
　　Ryu blames himself. He withdraws and starts leaning on alcohol. With the arrival of Arm, the grandson of the owner of the company where Ryu works, and their gradual relationship, Ryu's world begins to brighten again. When Ryu finds out that he has cancer and may not have long to live, Arm goes all in caring for him and the two decide to live together.
　　However, the world is always cruel. When Arm and Ryu learn the truth of something that tears them apart, Ryu disappears from Arm's life. Arm tries every 四大家族之龙虎兄弟means to find Ryu without any luck, until finally, Arm gets a box. This box contains all the answers.