SEE ALSO: Kang Ha Neul to sing the main characters' theme for 'Angel Eyes' OST

Kang Ha Neul sang the acoustic version of Baek Ah Yeon's previous OST song for the drama as the theme song for Lee Sang Yoon's character Park Dong Joo, whom he plays the younger version of. He also showed his support for the drama with his handwritten placard as well as through the making film for his cover.

Listen to Kang Ha Neul's soothing voice below!