Sunghoon was suffering from blood cancer and he kept it a secret from his girlfriend, he didn't want to worry her. Sunghoon always lied that he was busy working, even though he was undergoing chemotherapy at the hospital. Sunghoon told his best friend to take his place in the future after he died. He wants his girlfriend to be happy, so he brings his best friend closer to his own girlfriend. Sunghoon doesn't want his girlfriend to know about his illness.