Seongsu cheese katsu restaurant with spicy gyudon: Kosi Seongsu

Today I'm writing up my visit to Kosi Seongsu Branch 😋 This is an honest review, so if you're looking for tonkatsu or udon near Ttukseom/Seongsu, I think this'll be helpful!!

Where is Kosi Seongsu Branch? 2 minutes from Ttukseom Station Exit 6, and the seating

Kosi Seongsu Branch is a 2-minute walk from Ttukseom Station Exit 6.

The inside had an open kitchen, and besides 2- and 4-top tables, there were bar seats facing the kitchen, which looked great for solo dining without feeling self-conscious!

Ordering is set up so you pay directly at the kiosk, which was convenient 😀 If you want to pay with cash, just select the cash button and settle up on your way out!!

Kosi Seongsu Branch menu and prices

Cold udon and soba at Kosi Seongsu Branch 🥢

• ⭐️Bukkake udon (signature) ₩9,000 single / ₩14,000 set — a premium cold udon tossed in a special tsuyu made the traditional Sanuki way
• Toriten bukkake udon ₩11,000 single / ₩16,000 set — cold udon topped with crispy seasoned fried chicken thigh (toriten)
• Ten bukkake udon ₩11,000 single / ₩16,000 set — a signature cold udon topped with crispy tempura (1 shrimp, 1 kabocha)
• Zaru udon ₩9,500 single / ₩14,500 set — the classic chewy Sanuki-style noodles dipped in zaru dashi
• Zaru soba ₩10,500 single / ₩15,500 set — buckwheat noodles (판모밀) dipped in fragrant zaru dashi
• Kawa bukkake ₩12,000 single / ₩17,000 set — a special cold udon topped with savory, chewy chicken skin
• Sanuki-style mazeudon ₩11,000 — Japanese-style mixed noodles packed with umami from stir-fried minced meat and various toppings

Handmade tonkatsu, including the cheese katsu 🍽️

• Fresh pork loin tonkatsu ₩11,500 single / ₩15,000 set — domestic pork loin aged 24 hours, fried with milk and moist breadcrumbs
• Handmade cheese katsu ₩12,500 single / ₩16,000 set — the signature katsu, packed with 100% natural mozzarella over domestic pork
• Fresh pork loin half-and-half katsu ₩13,500 single / ₩17,000 set — a combo of pork loin tonkatsu and cheese katsu in one
• King shrimp katsu ₩12,000 single / ₩15,500 set — fresh king shrimp fried in moist breadcrumbs for a crispy katsu
• Fresh pork loin assorted katsu ₩14,500 single / ₩18,000 set — a generous set of pork loin tonkatsu plus 1 piece of king shrimp katsu

Hot udon and rice bowls, including the gyudon

• Kake udon (hot) ₩9,000 — a light udon based on a secret soy sauce brewed from kelp, anchovy, and mackerel flakes
• Ebi tempura udon ₩11,000 — hot udon topped with crispy fried shrimp
• Toriten udon (hot) ₩11,000 — a hearty hot udon topped with crispy-outside, juicy-inside fried chicken thigh
• Handmade katsudon ₩11,000 — a rice bowl with thick tonkatsu topped with special sauce and soft egg

We ordered three dishes that day — cheese katsu, zaru soba, and gyudon (beef rice bowl) !! Gyudon lets you choose the spice level, and we went with the spicy version 😋 You can also add extra tonkatsu separately, just so you know!

There's a review event too, so if you want to try the sides, make sure to apply for it !! The sides you can try through the review event were lotus root kushikatsu, vegetable tempura, and sweet potato cheese croquette 🤤🤤

Sides and extra portions

• Extra tonkatsu (120g) ₩6,000 — a popular add-on that lets you make an udon or rice bowl feel like a full set with a light side of katsu
• Fried chicken (karaage/toriten) ₩6,000 — crispy outside, juicy inside, pairs well with cool tsuyu from the cold udon
• Fried shrimp 1pc ₩2,000 / 2pc ₩4,000 — crispy Japanese-style snowflake-battered king shrimp (orderable from just 1 piece)
• Vegetable tempura (1pc) ₩2,000 — big, savory fried vegetable tempura, great dipped in hot udon broth or tsuyu
• Fried tofu sushi (2pc) ₩2,500 — sweet and salty plump inari sushi that adds a filling carb boost to the noodle dishes
• Sweet potato cheese croquette (2pc) ₩3,500 — a special side combining sweet potato mousse and soft cheese
• Lotus root kushikatsu (3pc) ₩4,000 — crunchy lotus root fried crisp on a skewer
• Whole squid rings (3pc) ₩4,000 — chewy whole squid fried until crispy

On the table there was a Japanese spicy powder (?) for adjusting the seasoning — I knew the name but forgot it haha.. there were also sesame seeds, pepper, and salad sauce, and apparently this place was featured on a TV show about masters of everyday life, which showed up on the monitor and got me even more excited 😮😮

How fast does the food arrive? Quick even when Kosi is full

Kosi Seongsu Branch was fairly full of customers, but the food still came out faster than expected (turnover seems to be good).

If you order the buckwheat noodles (zaru soba), fried tofu sushi comes along with it. Add green onion, grated radish, and wasabi to the tsuyu to taste!

Spicy gyudon ⭐️⭐️ — how hot is it really?

I chose 'spicy' for the gyudon spice level, and it delivers real heat! Even my boyfriend, who usually likes spicy food, said this one was solidly spicy haha. If you're sensitive to spice, go with 'regular.'

Cheese katsu ⭐️⭐️⭐️ — mozzarella that stretches and stretches

Look at that cheese stretch 🥹💕 It seems to use mozzarella — there's a lot of cheese and it stretches beautifully, so it seemed like a dish kids would love too. When you bite in, the crispy breadcrumb texture blends with the savory cheese and it's delicious! When it starts to feel a bit rich, dip it in the sauce that comes with it or add some wasabi ^^

Zaru soba ⭐️⭐️ — springy cold buckwheat noodles

The noodles didn't clump together and had a nice chewy texture! Mix grated radish and green onion into the tsuyu well, then dunk the buckwheat noodles in fully. The noodles were springy and the sauce was tasty!

Honest verdict on Kosi Seongsu Branch ⭐️⭐️⭐️ — a familiar taste that never misses

A place that's good for casually grabbing a meal, more than for a special occasion!

After finishing everything, my boyfriend and I both felt the same thing: "It's exactly the taste you'd expect, but reliably tasty without any misses!" It's the kind of taste that sticks faithfully to the formula of a franchise-style Japanese restaurant we all know well. From how crispy the cheese tonkatsu is, to the soba broth, to the seasoning on the rice bowl — nothing stands out as off, it's familiar and consistent, the kind of classic taste nobody would dislike.

So rather than for an anniversary or a blind date where you need to set a mood, I'd recommend coming here when you're stuck on "what should I eat for lunch/dinner today?" and want to fill up without any risk of disappointment!!

When is Kosi Seongsu Branch worth a visit?

• When nearby office workers or students want a quick meal at lunchtime
• When you want to step out in sweats on the weekend for clean, no-fuss Japanese food
• When the bar seating makes it easy to eat solo without feeling awkward
• When you're looking for a restaurant to bring kids to that avoids polarizing dishes

If any of these fit you, I'd recommend Kosi Seongsu Branch!😝🥄