Seongsu udon and tonkatsu spot with Sanuki fresh noodles: Kosi Seongsu

What is Kosi Seongsu Branch, the Sanuki udon and tonkatsu restaurant in Seongsu?

Kosi Seongsu Branch is a Japanese restaurant serving udon and tonkatsu at 31 Sangwon 1-gil, 1st floor, Seongdong-gu, Seoul. Yesterday I wanted proper Japanese food, so I headed to Kosi Seongsu Branch, known as one of the best tonkatsu spots in Seongsu. Turns out this place even appeared on the TV show Master in the House, and they use only handmade fresh noodles made in the 800-year-old Sanuki tradition. By the way, the name 'Kosi' is a Japanese word for the chewiness and springiness of noodles. Since the tonkatsu is also made only with domestic fresh pork loin, I went in with high expectations!

• 📍31 Sangwon 1-gil, 1st floor, Seongdong-gu, Seoul (2 free parking spots in front)
• Daily 11:00–21:00
• Break time 15:00–17:00
• Last order 20:30

The clean, warm wood-toned exterior stood out along with the tidy Japanese-style atmosphere. Seeing the appetizing photo signboard set up outside, I was already happily agonizing over what to order before even walking in.

Bar seats at Kosi Seongsu Branch that work for solo diners

Walking inside, there's a bar table along with comfortable seating, so it looked like a great spot to grab lunch or eat solo near Seongsu-dong without any pressure. I liked the overall pleasant and clean atmosphere.

How does the set menu work at Kosi Seongsu Branch?

You order through the kiosk at your table! What's especially appealing here is the set menu structure. If you order udon as your main, you can add crispy tonkatsu as a side, and conversely, if you order tonkatsu as your main, you can add udon to make it a hearty meal. Being able to reasonably taste both signature menu items made this feel like the top choice for value among Seongsu tonkatsu restaurants.

We ordered the signature bukkake udon as our main. My friend ordered just the bukkake udon on its own,

while I added the crispy tonkatsu on top. It came out on a neat tray packed full with sauce, salad, tonkatsu, and fried tofu rice balls — just looking at it felt filling. Even though I've been eating a lot less lately... just udon alone somehow wouldn't have been satisfying enough... adding the tonkatsu was a genius move!

The default salad sauce seemed to be a fruit-based dressing, and it was really refreshing. The dressing was also set out on the table so you could pour on as much as you wanted, which was another nice touch.👍

How were the bukkake udon noodles and tsuyu sauce?

The visual of the bukkake udon was insane! You just pour the tsuyu sauce generously over the noodles, which look plump and bouncy just from looking at them.

You mix it well with the tenkatsu (tempura bits), scallions, and grated radish that come with it by default! The moment I took my first bite of noodles, I couldn't help but be impressed. The bounciness and chewiness of the noodles were exactly like the texture I had in Japan. The noodles were soaked through with a savory, slightly salty tsuyu, giving a clean yet deep flavor.

Fresh pork loin tonkatsu and cheese croquette added to the set

The tonkatsu that came with the set held up in quality against dedicated handmade tonkatsu specialty shops. Living up to its reputation as a true Seongsu tonkatsu restaurant, the breading was as crispy as a cracker and the meat was thick with juices still intact. The meat was really thick so it had great bite, and the portion was generous — I really enjoyed it.

The cheese croquette served on the side was also so delicious! Being able to eat savory, crispy handmade tonkatsu together with chewy, cool bukkake udon at the same time!! The balance was perfect👍

Is Kosi Seongsu Branch worth a visit? Final verdict

Thanks to the thick tonkatsu, I felt satisfyingly full, and combined with the perfect texture of the noodles, this is a place I'd definitely recommend ordering as a set among Seongsu tonkatsu restaurants! It's a restaurant that has all three elements down — taste, portion, and price — so I think I'll be visiting often whenever I go to Seongsu-dong from now on. If you want to enjoy thick, crispy handmade cutlets and chewy noodles all at once, be sure to visit Kosi Seongsu Branch, a Seongsu tonkatsu restaurant!