Ttukseom Station tonkatsu dinner with no wait for cheese katsu: Kosi

Kosi Seongsu Branch: cheese katsu and chewy udon near Ttukseom Station

Every time I passed by Kosi Seongsu Branch in Seongsu, there was always a line at lunchtime! I kept wondering just how good it could be for people to line up like that. This time I aimed for what seemed like a quieter dinner slot and finally visited.

To cut to the conclusion: the tonkatsu was great, but honestly it was the udon noodles I remember most from this tonkatsu spot near Ttukseom Station.

Where is Kosi Seongsu Branch, and is there parking?

Kosi Seongsu Branch was really close — about a one-minute walk from Exit 6 of Ttukseom Station. It's also around five minutes from Exit 1 of Seoul Forest Station, so it's a convenient spot to grab a meal after hanging out at Seoul Forest or the Seongsu-dong café street.

I'd always seen a long line at lunch, but visiting a bit past 6:30 pm meant I luckily got seated with no wait at all. Up to two cars can park for free for one hour right in front of the restaurant, and if that's full, you can use the public parking lots at Seongsu Culture & Welfare Center or Seongdong Gu Community Sports Center.

Inside Kosi Seongsu Branch: clean, comfortable and plenty of solo seats

Tonkatsu places that fry constantly can sometimes hit you with a strong oil smell the moment you walk in. But the air at Kosi Seongsu Branch was fresh and the space overall felt clean, which made a great first impression. The tables were also spacious enough that ordering several dishes didn't feel cramped.

Seating ranged from group tables to comfortable solo seats. At some restaurants a solo seat barely fits a water glass, but here the tables had generous space, making it a good option for a solo lunch too. Ordering was done through a tablet at each table, and payment could be completed the same way, which was convenient.

What we ordered at Kosi Seongsu Branch and what it cost

Kosi Seongsu Branch is a Japanese restaurant specializing in udon and tonkatsu. Here's what we ordered that day.

• Spicy katsudon + added kake udon ₩14,500
• Cheese katsu + added kake udon ₩16,000
• Inari sushi (2 pieces) ₩2,500
• Pepsi Zero ₩2,000

We went for the tonkatsu, so I focused on katsu dishes — and only after ordering did I find out Kosi was featured on SBS's Masters of Living (생활의 달인) for its udon! It turns out this is a Konkuk University spot famous for its line-worthy cold udon and fresh pork loin tonkatsu, and Seongsu is its directly-run branch. Actor Kim Seung-soo apparently visited and raved about it, so it's also known as a Kim Seung-soo favorite.

If I'd known, I would have ordered the main udon separately haha! This time I made do with the added kake udon in the set, but next visit I'm definitely ordering the udon as the main dish.

Kake udon: plump, chewy 48-hour aged fresh noodles

I assumed an udon added to a set would come in a tiny portion, but the bowl was bigger and the amount was quite generous. Eating it alongside the tonkatsu and katsudon left us more than stuffed. The added udon didn't come with the noodles prettily coiled like the main dish does, but the taste exceeded expectations.

Even when I lived in Japan, I always preferred udon over ramen. Kosi's udon noodles were genuinely plump and chewy. The bounce you feel when chewing was so distinct that the noodles alone were delicious.

Kosi apparently uses fresh noodles made the traditional Sanuki way — kneaded from just salt, water, and flour, then aged twice over 48 hours before they're ready. In Japanese, when noodles have that springy, chewy bite, it's described as having 'koshi' — and true to the restaurant's name, the noodles really did have proper koshi. The broth had great depth too, so I kept spooning it up.

Cheese katsu packed with melted cheese

The cheese katsu was generously stuffed with mozzarella. When cut in half, the inside was completely filled with cheese, which should satisfy anyone who loves cheese.

The batter was crisp and the meat was juicy, so the texture combination was great too. Kosi apparently pounds domestic fresh pork loin by hand every day and fries it to order, which is probably why the tonkatsu wasn't dry at all.

The cabbage that came with it was refreshing with the sauce drizzled on, good for pairing between bites of the fried katsu. Pepper and shichimi were also set out on the table, so you could add more seasoning to taste.

Spicy katsudon: better for the heat

For the katsudon, I chose the spicy version instead of the regular one — and it was genuinely spicier than I expected! A typical katsudon leans sweet and mild, which can get a little heavy after a while, but adding spice here made it even more delicious.

It was the kind of spice that grabs your appetite, so I never got tired of it all the way through. It's not easy to find katsudon this spicy in Japan, so I liked that it was properly spiced to suit Korean tastes 🔥

Inari sushi, the perfect side at Kosi Seongsu Branch

The inari sushi (fried tofu pocket rice) we ordered as a side wasn't just a small token dish either. Each piece was plump and generously filled, making it a nice bite between the tonkatsu and udon. At ₩2,500 for two pieces, it was an easy add-on, and it could work as a hearty side for anyone who wants a bit more food.

Is Kosi Seongsu Branch worth a visit? Final verdict

Trying it myself, I could kind of understand why there's always a line at lunch. The tonkatsu had crisp batter and juicy meat, and above all, the plump, springy udon noodles made with 48-hour aged fresh noodles were memorable. Adding kake udon to the tonkatsu made the portion quite filling, so it was a good option when looking for a hearty, good-value meal in Seongsu.

The space was clean and had both solo and group seating, so it looked well-suited for solo dining, lunch with friends, or a meal on a Seoul Forest date. Next time, instead of focusing only on tonkatsu, I definitely want to order the main udon or cold udon that was featured on Masters of Living. If you want chewy udon and crispy tonkatsu together near Ttukseom Station, Kosi Seongsu Branch is worth a stop!