Seo In-guk at 15 Acting Years: The Finale 'I Love You' Was His Own Idea

Fifteen years into his acting career, Seo In-guk has a confession about the finale of I'll Go to Work Tomorrow: the line that closed the show was entirely his own idea.

The tvN office romance, which wrapped its run recently, starred Seo as Kang Si-woo, a team leader at a fictional electronics company whose nickname among colleagues translates loosely as "the No-Man" (no smile, no people, no sorry). The original script called for the two leads to exchange rings and walk away. Seo wanted something more definitive. "I wanted a clear ending," he said at a Seoul café interview on July 29, "so I improvised 'I love you' on the spot. The director loved it, and Ji-hyun received it well. That stayed with me."

The role required Seo to suppress almost every instinct he has as a performer. Kang Si-woo organizes his entire home around work appliances and fills every waking hour with tasks. "I couldn't understand a life like that," Seo said, "but I found it admirable and fascinating. I had zero in common with him. I don't think I could live that way for a single day."

Physically, he worked to match the character's rigid bearing: straightening his posture, correcting his forward head position, rethinking his walk. "My natural resting face already reads as slightly pouty," he admitted, "but I had to push further, to look harder."

The drama is based on a webtoon of the same name and follows seven-year office veteran Cha Ji-yoon (Park Ji-hyun) as she and the exacting Kang Si-woo become indispensable to each other. Seo praised Park Ji-hyun as a collaborator with few limits: "She absorbs ideas actively and has a wide emotional range. Because she was so open, I could be bolder."

This is Seo's third consecutive office-set project. Before I'll Go to Work Tomorrow came the Netflix series My Boyfriend, where he starred opposite BLACKPINK's Jisoo, and next on his schedule is another tvN office drama, The Employee Who Sees Fate. He insists the pattern was not deliberate. "I just kept finding scripts I liked. It wasn't a strategy." That said, he has a theory about why the genre keeps pulling him in: "There's a particular kind of appeal in watching someone fully absorbed in their work. And the tension of an office romance, that specific precariousness, is something only this genre delivers."

He draws a clear line between his two recent office leading men. Park Gyeong-nam from My Boyfriend was thorough, but Kang Si-woo operates inside a near-perfect daily routine. "Kang Si-woo waits for the other person, considers them, sacrifices for them. He's more grown-up, more self-effacing."

The scene he remembers most vividly from the shoot is, fittingly, the finale. The crew had a narrow window of roughly two hours before the light was gone on a very cold day. "We had to capture the sky just before sunset," he said. "It was frantic and beautiful."

Seo got his start winning Superstar K on Mnet in 2009 and has worked continuously since, across music, drama, and variety. He recently appeared as a panel guest on the Netflix reality show Never Been in a Relationship But Want to Fall in Love 2. Asked why he takes on so much across so many formats, he was direct: "I'm genuinely greedy. I find more pleasure in working than in a long vacation." He also points to his fans as a sustained motivation, noting that people who watch his dramas, stream his music, and travel to overseas fan meetings are the reason he feels he exists in the industry at all. "I want to keep showing them something good. That sense of gratitude keeps me going."

Born in 1987 and approaching his forties, Seo says his goal is simply to keep meeting roles that fit wherever he is in life. He traces a line through his career: Reply 1997 and High School King of Savvy in his twenties, Hundreds of Millions of Stars from the Sky in his thirties. "Every decade I've found something that felt natural for that age," he said. "I want to keep doing that. There are still so many jobs, personalities, and stories in this world that I haven't played yet." At fifteen acting years, the ceiling, by his own measure, is still a long way off.