Kim Kyungsoo and Kim Jongin are lovely siblings. Kim Jongin (younger brother) very popular in school, always spoiled by her brother, Kim Kyungsoo. Their family, whose status is rich, makes Doh Taemin his rival ( Kyungsoo classmates)  jealous and bully Kyungsoo.

When Kim Kyungsoo gets hit by a car and needs a blood transfusion, it is found out that Kyungsoo is not the Kim’s biological son. And real son is Doh Taemin. This  happened because Kim Jongin dad wants pay debt to Doh family because Mr Doh dead accidentally got hit by Kim’s car when Kyungsoo age (5 months). Their sons return to their original birth parents. Shortly after they switch back in hospital, the Kim’s family moves to Japan and Doh Kyungsoo loses his memories because cannot accept Kim Jongin left him.

Eight years later, Kim Jongin returns to South Korea as a successful Dancer from Japan. He returns to Korea with his fiancée, Moonkyu. While Doh Kyungsoo changed his name D.O. popular soloist in Korea  and engaged with his best friend Park Chanyeol. Park Chanyeol cannot accept his best friend Kyungsoo got sick (diagnosis cancer). He want to marry Doh Kyungsoo to give his best friend chance to feel ‘LOVE’ before Kyungsoo die.