Yim Si-wan’s latest thriller film, “Unlocked,” depicts the 34-year-old actor as psychopathic killer Jun-young, who hacks into Na-mi's (Chun Woo-hee) smartphone and later threatens to kill her. It’s hard to imagine the actor, who started out in entertainment as part of idol boy band ZE:A and usually exudes a prince charming image, as a ruthless villain. But Yim said it was not difficult to...