Mu-jin is the adopted brother of Sim Jae-yi. After the original Hongrang disappears, the family adopts Mu-jin. He is portrayed as a loyal, dependable figure who stands by Jae-yi. A man claiming to be the missing heir, Hongrang, returns to his family. As the drama unfolds, Mu-jin becomes suspicious of the man returning as Hongrang and schemes to expose his true identity.