Marriage Blue is a romantic comedy film that follows the misadventures of four engaged couples in the week leading up to their weddings. Tae-kyu is a former professional baseball player who currently coaches for a minor league team. His girlfriend Joo-young runs a successful urology clinic. They've broken up once before then gotten back together, and now they're about to get married. But a week before their wedding, Tae-kyu learns something about Joo-young that makes him feel betrayed and jealous. Growing increasingly neurotic, he becomes obsessed with finding all about her exes and dating past. Chef Won-chul and nail artist So-mi have been a couple for seven years and their wedding day is fast approaching. But feeling that something is missing in their life, So-mi suspects that Won-chul doesn't feel passionate towards her anymore and merely regards their relationship as a comfortable living arrangement. Several days before getting hitched, So-mi travels to Jeju Island for a nail art competition, and there she meets and becomes attracted to Kyung-soo, a tour guide and web comic writer. Geon-ho is a sweet, middle-aged bachelor who owns a flower shop, and he's about to marry Vika, who hails from Uzbekistan. When Geon-ho is suddenly afflicted with erectile dysfunction, he goes to see Joo-young, a urologist, who tells him that there's nothing wrong with him physically and his impotency may be caused by stress. Since Vika is beautiful and much younger than him, Geon-ho struggles with feelings of inadequacy and starts to wonder if she's only marrying him to attain Korean citizenship. Dae-bok works at Joo-young's urology clinic. He's recently began dating Yi-ra, a wedding planner. Then one day, during a baseball game, Yi-ra tells him that she's pregnant, and Dae-bok immediately proposes. But as they prepare for their wedding, they keep arguing constantly. It isn't that Dae-bok is scared of becoming a father, but he senses from Yi-ra's cynical attitude that she doesn't feel their relationship has any kind of long-term future, so he desperately tries to change her mind.