Eun, See-Joon
Se-wa's twin brother who, when in public, acts embarrassed and disapproving of Se-wa's clingy affection for him, although his true feelings are conflicted. To distance himself from his sister, Se-Joon gets a girlfriend named Su-In. When Se-Wa had her heart transplant, Se-Joon became incredibly lonely because of her absence and decided that he would make her fall in love with him so that she would always be with him from then on. He spread rumors about Se-Wa to isolate her so that she would rely solely on him. When Se-wa started hanging around Gi-Hoon, Se-Joon became very jealous and starting investigating Gi-Hoon's past, ultimately revealing Gi-Hoon's secret.