The Smile Has Left Your Eyes (하늘에서 내리는 일억개의 별) (2018)

A detective takes on a murder case that was disguised as suicide and becomes obsessed with solving it. But his younger sister falls in love with a man that is somehow connected to the murder. The detective tries to push the two away from each other, because he knows the man isn't a good person but the young woman has sympathy for him.