Seongsu udon restaurant, 5 dishes for two at mid-30,000 won: Kosi

Today I visited Kosi, a handmade udon and tonkatsu specialist in Seongsu, known for great tonkatsu! I'd ordered delivery from another branch many times but this was my first time actually visiting a Kosi restaurant, so I came in with high expectations — and it exceeded them, haha!

Where is Kosi Seongsu Branch, and what are its hours?

• Address: 31 Sangwon 1-gil, 1st floor, Seongdong-gu, Seoul, South Korea
• Hours: Daily 11:00–21:00
• Break time 15:00–17:00 / Last order 20:30
• Takeout, delivery, groups, reservations, and parking all available

This Seongsu tonkatsu favorite, Kosi Seongsu Branch, is actually closer to Ttukseom Station than Seongsu Station. It's not crowded at all, so the alley has a relaxed, quiet vibe that made it much easier to find — a lot more pleasant than the busy main streets. There's parking for up to 2 cars right in front too, so it's easy to get to whether you drive or take transit!

Does Kosi Seongsu Branch have seats for solo diners?

Inside, Kosi Seongsu Branch has not just solo seats but 2-person and 4-person tables too, so it felt comfortable whether you come alone or with a group. It'd be a great spot if you're in Seongsu or Ttukseom and hesitating over eating alone.

From their signature cold udon to hot udon, tonkatsu, and donburi (rice bowl), they had a range of Japanese dishes, plus plenty of sides to order to your taste.

Review event: pick a fried side at Kosi Seongsu Branch

They were also running a Naver review event, and instead of just one fixed item, you could choose from several options like lotus root kushikatsu (skewered fried lotus root) or croquette. Most places just give you a drink, so being able to pick a fried side you actually like felt like a real bonus! Definitely take part if you visit.

Two mains and three sides for two: mid 30,000 won

We came as two people — 2 mains, 3 sides, right? There was so much I wanted to try that we ordered all of it, and even so the total came out to just mid ₩30,000s! With value like that, there's really no reason not to come here...

Each table had salad dressing and the necessary cutlery neatly set out. It was nice being able to pour on as much dressing as you liked, and the cutlery and table were spotlessly clean, which was a great first impression.

A complimentary cheese sweet potato croquette on the house.. it's a small thing, but it really made my day!

The full order at Kosi Seongsu Branch

• Half-and-half katsu
• Lotus root kushikatsu
• Tori-ten bukkake udon
• Squid rings

Half-and-half katsu: tonkatsu and cheese katsu on one plate

The half-and-half katsu at Kosi Seongsu Branch pairs regular tonkatsu with cheese katsu, so you get both the light, crispy classic and the rich, savory cheese version — a total two-birds-one-stone dish! If you can't decide, half-and-half is the way to go.

Look at that cheese pull. It just kept stretching endlessly, and the visual alone was amazing! Crispy on the outside, packed full of mozzarella on the inside — I let out a gasp with the very first bite.

The tonkatsu wasn't dry at all and had no off smell, so you could really feel how juicy it was. The breading had zero stale-oil smell and stayed crispy all the way through — a little salt or wasabi on top made it taste incredible.

Tori-ten bukkake udon: 3 pieces of fried chicken and sanuki noodles

For the tori-ten bukkake udon, the noodles and tsuyu (dipping/soup broth) came separately, and it also came with one piece of inari (fried tofu pouch) sushi!

There were three big pieces of fried chicken on top. It had a strong handmade fried chicken feel, worlds apart from your average karaage — crispy outside, juicy inside, and the juices burst out the moment you bit in! The seasoning was perfectly salty too, an absolutely dreamy match with the udon noodles.

Kosi's noodles are made using the Udong Wanggun traditional sanuki method, so the udon strands had a real chewy, springy bounce. Pouring the cool tsuyu over them kept that bouncy, chewy texture alive all the way to the last strand — I finished it without getting tired of it once.

The 4,000 won sides: lotus root kushikatsu, shrimp tempura, squid rings

The sides we ordered separately — lotus root kushikatsu and shrimp tempura, plus squid rings (not pictured) — were all ₩4,000 each, which felt hard to believe given the quality. True to its reputation as a Seongsu tonkatsu favorite, the breading was thin and crispy so nothing felt greasy, and the natural flavor of each ingredient really came through. The crunchy lotus root and the springy squid rings especially were great little bites to snack on between mains.

After only ever having it delivered, eating fresh-fried katsu and bouncy handmade udon straight from the kitchen at Kosi Seongsu Branch was so much more delicious and satisfying! Great value, a comfortable atmosphere — I genuinely recommend it if you're looking for a proper Japanese tonkatsu and udon spot in Seongsu or Ttukseom!