Han PD talked about casting the stars, saying, "I believed that we cast a group of actors who were suitable for the roles, instead of looking at their movie star reputations."

The director continued to describe, "I had the impression that Park Joong Joon sunbaenim would be a great captain in leading 'Bad Guys'...I watched him on the big screen growing up and I'm truly delighted to be able to work with such a legendary actor. Both Joo Jin Mo and Kim Moo Yeol were full of charm as well. As for Ji Soo, I thought 'He looks charming for a guy of a younger generation.'"

SEE ALSO: 'Running Man' cast shocked by the state of Kim Jong Kook's overwhelmingly messy home as they help clean up

Undergoing a drastic transformation, Ji Soo mentioned, "It was a difficult role to play so I wanted to challenge myself. Since I couldn't do it myself, I relied a lot on the director and fellow cast/staff members on set."

Ji Soo described his tough character as someone with "A kind heart. He has this strong urge to protect his one and only sibling. The story unfolds as he tried to protect those he loves and the main focus will be the necessary measures he takes to protect his sibling.  I actually don't have a younger brother/sister in real life so I look up to my noona instead."

Meanwhile, fans can expect OCN's new thriller to air its first episode on December 16.