Character Arc
Ko Nak-jun is Lee Hae-sook's devoted husband, who died years before her and has spent the intervening time in heaven waiting for her arrival. When he is finally reunited with Hae-sook, he appears as his young, thirty-something self, a choice rooted in promises the couple exchanged during their marriage and in his wish to greet her at the prime of the man she once fell in love with. In the afterlife he works as a kind of heavenly postman, delivering wishes and letters that pass between the living and the dead, a role that keeps him moving through the drama's gently bureaucratic vision of the world beyond.
Nak-jun's central conflict grows out of the mismatch his choice creates: he is young while Hae-sook is old, and the visible gap between them forces both husband and wife to confront what their bond truly rests on. His love is presented as patient, steady and almost stubbornly loyal, and much of his arc involves protecting Hae-sook, bending heaven's rules to stay near her, and helping her work through the unresolved memories and mysteries that surface after her arrival. His devotion serves as the counterweight to Hae-sook's self-acceptance, the two together forming the show's portrait of a marriage that outlasts death.
Son Suk-ku plays Nak-jun with the understated intensity that has become his trademark, balancing tenderness, quiet humor and longing. The role marks a softer, more romantic register for an actor better known for thrillers and dramas such as D.P., My Liberation Notes and Big Bet. (Character details flagged for fact-check given the show's recent release.)