[Interview] Completing the Most Brilliant Finale of a Long Journey! 'Yumi's Cells 3' Kim Jae-won ①

In the Sun-rok Cell Village, a solid "Pillar of Principles" stands tall and straight. Small yet weighty rules like "wash your hair first when you shower" and "limit hobby spending to a maximum of 500,000 won per month" form the foundation of Sun-rok Cell Village and are what keep its peace intact.

Actor Kim Jae-won's own Pillar of Principles seems densely packed with major and minor rules branching from the grand rule of "always give your best in every moment." "Love the projects I take on," "show a new side each time," "treat every project with deep responsibility," and similar tenets have guided Kim's choices the way the Sun-rok principles shape the order of the cell village.

From the verdant youth Choi Han-soo in 〈Our Blues〉, to the transgender Cheon Sang-hak in 〈Eun-joong and Sang-yeon〉, to host-bar pro Kang Ji-hwon in 〈Lady Dua〉, Kim Jae-won has made bold, fearless choices compared with many of his peers. In the process, he left another striking mark on his filmography with the role of Shin Sun-rok in 〈Yumi's Cells〉 Season 3 (hereafter 〈Yumi's Cells 3〉).

The Tving Original 〈Yumi's Cells〉 series concluded its long journey with Season 3, following Seasons 1 and 2. The recently finished 〈Yumi's Cells 3〉, which wrapped on the 4th, tells the story of the younger man Shin Sun-rok (Kim Jae-won), who drops into the unstimulating routine of star writer Yumi (Kim Go-eun) like a suddenly thrown stone. After Gu-woong (Ahn Bo-hyun) in Season 1 and Yu-babi (Park Jin-young) in Season 2, Yumi finally promises a lifetime with Sun-rok. Viewers who have watched Yumi’s coming-of-age and love story over the years could finally send Yumi off with relief at this happy ending with Sun-rok. This bittersweet season, like sending off a beloved friend, reached its perfect finale thanks to Kim Jae-won’s Shin Sun-rok. On the 8th, Cineplay met Kim Jae-won at an undisclosed location in Jongno-gu, Seoul, to talk about the finale of 〈Yumi's Cells 3〉, behind-the-scenes moments, and his mindset as an actor. Below is the full interview transcript.

First, how do you feel now that this series has ended after drawing so much attention?

〈Yumi's Cells〉 has been a long journey through Seasons 1, 2, and 3, and I'm so proud to have been part of bringing that journey to a close—and to feel like we closed it well. I'm extremely happy and grateful for all the interest and love. I use a communication app called Bubble, and I felt so sad to see 〈Yumi's Cells 3〉 end that I even wrote a long letter there. It was a character I grew attached to more than I expected. I really hope Sun-rok and Yumi live very happily. As a longtime viewer who has followed 〈Yumi's Cells〉 from Yumi’s perspective, I truly want Yumi to live a happy life forever.

The role of Shin Sun-rok was heavily fan-cast from the webtoon onward, so expectations were high. Carrying the title of the "perfect younger man" must have felt pressuring—how did you feel when you finally got the role?

It would be a lie to say I felt no pressure. It felt like being the boyfriend of a beloved daughter from a big family, introduced to all the relatives over the holidays. In the original, Sun-rok is almost a unicorn among younger men—flawless and without excess—so that brought a certain pressure. But on the flip side, I thought how incredible it was to have the opportunity to play such a fantasy character. I worked very hard preparing; whereas I always do my best, for this role it felt like I prepared 200% for something I wanted to give 100% of myself to.

Compared to previous seasons, the eight-episode length of 〈Yumi's Cells 3〉 might feel a bit short. Did you feel there were parts of Sun-rok’s story that weren’t fully explored?

As actors, we perform what's given; we can't adjust a show's length. I wondered why Season 3 was shorter than the earlier seasons. Not that it's a fact from the director or writer, but personally I thought Sun-rok is different from the previous characters in that once he’s certain, he goes straight ahead. Because he doesn’t hesitate or calculate, there’s no need to stretch his arc—his character is naturally compact. For me, even if it was short, my priority was to express Sun-rok well, so I gave the role my all.

After passing through Gu-woong and Yu-babi, Sun-rok became Yumi’s final partner. In your view, what was the decisive reason Sun-rok became Yumi’s partner? What is Sun-rok’s defining trait as you interpret it?

I thought about that a lot while acting. Sun-rok’s biggest charm isn’t the unicorn-like aura people mention or his height. It’s that the moment he’s certain, he just goes straight ahead. Other characters have hesitated in the face of reality, and maybe Sun-rok had doubts too, but once he decides, it’s like he’s on a single-track mission: “I love this woman, I will protect Yumi for life,” and then he keeps going without calculation. That willingness to go all the way is probably the biggest reason he reaches marriage. Also, I think Sun-rok must have felt a spark, an intense bolt of attraction—like falling for Yumi’s careless smile on the train.

I was struck by how Sun-rok is icy-cool at work but completely disarmed at home—his on-and-off switch was distinctive. You must have thought about syncing with the original material.

I focused on the appearance first. At work, Sun-rok wears his hair slicked back, square glasses, and looks cold; off the clock he's curly-haired, with his hair down and in pajamas, taking relaxed poses he would never show at the office. In real life I’m not a homebody at all, but I do have moments when I feel drained after work. I felt those parts matched closely, so I blended pieces of my real self into Sun-rok. I didn’t feel any major disconnect in sync with the original.

After playing Shin Sun-rok, you must have seen memorable viewer reactions. And because Sun-rok was a popular character in the original, how did friends and acquaintances react when you were cast?

People saying, "I want to meet a younger man like that" felt really good. My older sister liked Sun-rok so much that when she said, "At this level, it's acceptable," I thought, "I did well; it wasn’t bad." Before I played Sun-rok, my sister told me, "Do a good job." It had a bit of weight to it—like, “Do it well.” (laughs)

Many praised you for portraying the character with a restrained, understated approach. What did you focus on most when playing Sun-rok?

The first rule was: don’t be cheesy. As a younger man meant to inspire romantic feelings, he had to seem like a man, to create fluttering feelings, but never cross into being cheesy. There’s a fine line between cheesy and romantic. Given that this drama features cells that express inner feelings, I thought even if I remained expressionless, the cells would voice his heart. So I focused on keeping my expressions restrained and understated, letting the cells voice his inner feelings; I worked to strip back my performance and keep things simple.

The making-of showed you crying behind the camera after filming a confession scene. When emotions ran high like that, how did you keep your performance restrained on set?

When I went too far, the director corrected me right away. I tried to stay understated even in rehearsals, but some of the bold speech patterns from my previous role in 〈Lady Dua〉 slipped out at times. Go-eun kindly suggested different approaches like, "How about trying it this way?" But she never told me, "Do it like this because Sun-rok is this kind of character." She always respected the junior’s opinion. She’d ask, "What do you think?" and then we’d take the best of my ideas and shape them together. When I started to stick out in tone, the director and seniors reined me in; when I felt a scene could go a little deeper, I approached the director and suggested, "Could we go a bit more into it here?" That’s how some of the confession scenes came to be. In confession scenes, the rational person collapses and focuses on emotion, so I think Sun-rok’s reddened eyes were a natural expression of that. I remember tearing up without realizing it; watching the making-of made me realize how immersed I was in those moments.

There’s a line where Yumi says, "Sun-rok is MZ." From the perspective of an actual MZ generation member, were there parts of Sun-rok you didn’t understand or features you wanted to push further?

Role-play scenes can be polarizing and aren’t exactly ordinary. There were moments that felt embarrassing while acting, but looking back, I think those scenes amplify the appeal of the younger boyfriend. I felt awkward and shy in some takes and went back for retakes, but in the cinema scene I actually had fun and even suggested ideas. In real life I’d struggle with so much role-playing, though. (laughs)

The early "strawberry cream-filled fish-shaped pastry" incident was memorable too. Sun-rok bought all the remaining strawberry cream-filled fish-shaped pastries in front of Yumi. What was Sun-rok thinking in that moment as you acted it?

I haven’t asked the director about that yet, but I think the simplest conclusion is: Sun-rok wanted the strawberry cream-filled fish-shaped pastry. Although the show opens with a "hate-to-love" (enemies-to-lovers) concept from Yumi's perspective, from Sun-rok’s viewpoint it didn’t seem like that. He always treated Yumi rationally, and with the pastry incident he probably just thought, "I got here first, so I’ll take it." Early on there was also the Maltese incident with Yumi and Sun-rok. Funny side note: recently a lot of people set their profile pictures on my Instagram to Maltese dogs. (laughs)

Sun-rok proposes with a diamond ring only a month into dating, which isn’t easy in reality. Why do you think he could do that?

I don’t think it was an easy decision, but after showing how certain he was, he even says, "If it’s too much, you can return the ring," which shows how uncalculated Sun-rok is. He’s straightforward and clear, with no manipulation, and that makes him attractive. Seeing that he’d never done anything like that before, you think: how much must he have loved her to take that step? It’s very romantic.

How would you define the man Shin Sun-rok is?

I think he’s a "go-straight" guy. These days people talk about labels like "egen-nam" and "teto-nam." "Egen-nam" refers to the idealized, flawless "perfect boyfriend" image, while "teto-nam" describes a tough, straightforward type. Maybe Sun-rok is more of the latter. On the surface he might look like the stereotypical "perfect boyfriend," but I think a true "tough, straightforward" type isn’t about muscles or a deep, cavernous voice—it’s those single-minded, decisive, manly moments. That steady, determined spirit in a younger man is what I found attractive.

When did Sun-rok first open his heart to Yumi? In your opinion, when did his love actually begin?

When Sun-rok confesses he says something like, "Maybe I liked the writer from the beginning." Because he strictly separates work and personal life, he probably suppressed his feelings, but perhaps he had a crush on Yumi from early on and kept wanting to look out for her. Even though he had a rule of never dating work colleagues, his love grew despite himself. As if you could see through him with an X-ray, I think feelings he himself hadn't recognized were growing quickly without him even realizing it.

▶〈Yumi's Cells 3〉 Actor Kim Jae-won's interview continues in Part 2.