Dongjak udon restaurant with tableside kiosk ordering: Kosi Isu Branch

The food is amazing, but the service and how they treat customers is even more impressive — a waiting-line favorite near Isu Station 🌟

Today I'm sharing my review of "Kosi Isu Branch," a great Japanese restaurant for solo dining in Sadang 🌟 Even on a weekday lunch, even with a large dining room, the wait never lets up, and the friendly staff make it a standout lunch spot for office workers around Isu Station. Let's get into the detailed review of "Kosi Isu Branch" in Sadang/Isu Station ➡️

Where is Kosi Isu Branch, and what are the hours?

• ⏰️ Open daily 11:20–21:00 (last order 30 min before close)
• Break time 15:20–17:00
• 📍 2-minute walk from Isu Station
• 🚗 Free parking available

What's on the menu at Kosi Isu Branch? 📓

There's a menu board outside the restaurant too, which was nice to check while waiting — udon, tonkatsu, and donburi dishes are all on offer ✔️ There's actually more variety than what's listed on Naver Place — besides what's in the photo above, you can add tenpura to udon for 4,000 won, plus there's mini tonkatsu, cold soba, and more, so it's worth checking the menu again in-store 📓

Orders are placed via the kiosk at each table, and you can pay right there too — very convenient 👍

What we ordered for weekday lunch

• Mixed tonkatsu, single order (₩14,500)
• Toriten bukkake udon (₩11,000) + tenpura set add-on (₩4,000)
• Sweet potato cheese croquette, 2p (₩3,500)

The side dishes that come with every order 🌿

Every table has a sesame grinder, salt & pepper, and hot sauce on hand ✔️

You can also use the staff-call function on the kiosk — I liked that you can request free rice, cabbage, sauces, water, and other side items right through it 👍

Toriten bukkake udon with the tenpura set add-on 🍜

Kosi Isu Branch's toriten bukkake udon is a cold udon topped with three pieces of chicken thigh karaage 🐔 The side dishes are pickled radish, kkakdugi (cubed radish kimchi), and cabbage salad 🌿

The chilled broth doesn't come poured over the noodles — it's served separately, and staff kindly explained to pour it over the noodles when the dish arrived. Looking closely, the udon is neatly plated, topped with karaage plus scallions, seaweed flakes, tempura crumbs, lemon, grated radish, and ginger ✔️

The udon noodles at Kosi Isu Branch were chewy and springy with a nutty flavor ✨️ At some udon places, the cold noodles are so firm it's disappointing, but here the noodles were cooked just right — not undercooked, not mushy 👍 The light, chilled broth wasn't too salty and had great umami, and the coolness of the radish along with the subtle ginger note gave the broth extra depth!

There were three generously sized pieces of karaage on top, chilled to about the same temperature as the cold udon (probably to keep the udon from warming up). It was cold but had zero gamey or oily chicken smell, and even though it's thigh meat, it wasn't greasy at all — the light, tender flavor paired really well with the cold udon ✨️

The tenpura set comes with one inari sushi (fried tofu pocket rice), two fried shrimp, and fried sweet potato, kabocha squash, and perilla leaf. It's 1,000 won cheaper than ordering it à la carte, though the composition is slightly different ✔️

The inari sushi was salty-sweet but the rice wasn't dry — nice and soft, and the kabocha and sweet potato tempura had that natural sweetness that paired well with the batter ❤️ The best of all was the fried shrimp — thin, crispy, golden batter with plump, springy shrimp inside was truly excellent 🍤

A tip for eating the tenpura 💡

Eat the tenpura as fast as you can! It's freshly fried, super crispy and warm right out of the fryer, but thin items like the perilla leaf cool down fast, and you lose that first-bite magic if you wait 😢

The soy dipping sauce for the tenpura was also really good — just the right amount of salty-sweet, which paired well with the crispy batter ✨️

The tenpura set's quality made the 4,000-won add-on feel like a bargain 😀

Mixed tonkatsu à la carte, 14,500 won 🐖

Next up, mixed tonkatsu — comes with a pork loin cutlet, one shrimp cutlet, broth, sauces, and side dishes 🐖

First, the shrimp — this isn't a small shrimp, it's king shrimp, so big it didn't even fit in the photo 🦐 There's actually a king shrimp katsu menu with two shrimp, but it looked pricier so I went with the mixed katsu instead — and honestly, at this size, that's incredible value (the shrimp was longer than the entire tonkatsu). The flesh inside wasn't dry at all — light and tender, and it was the best thing I ate at Kosi Isu Branch 🌟

The tonkatsu came as one big cutlet sliced into 6 pieces, with a really thin batter that emphasized a light flavor over greasiness 🌟 As you can see in the photo, there's barely any oil, but oddly enough it wasn't dry at all — soft and tender to bite, with a strong, rich meat flavor.

It's delicious plain, but eating it with the pink salt and sharp wasabi provided, or dipping it in the tonkatsu sauce, brought out even deeper flavor ✨️ (Personally, I highly recommend the pink salt + wasabi combo!)

Sweet potato cheese croquettes, 2 pieces for 3,500 won 🍠

Two sweet potato cheese croquettes came along too — freshly fried and much hotter than they look 🔥

Like the other dishes, the batter here is thin, and it's generously packed with sweet potato and cheese! Inside the sweet, mousse-like sweet potato filling there's a good amount of cheese that stretches when pulled 🧀

The sweet, savory flavor was so good ❤️

Inside the restaurant, and how long is the wait? 🖼

The restaurant is located in an alley two minutes' walk from Isu Station 🚶‍♀️ There are chairs outside next to the menu board to wait in. To join the waitlist, you have to go inside and write your name on the list 📓

The inside was quite spacious, but there were so many customers I couldn't get a shot of the back of the restaurant 😢 Besides the seats in the photo, there are around 5-6 more tables, so it works for solo diners, couples, and groups near Isu Station! (There was a group of 6 who looked like coworkers eating together.) With so many customers, waiting is pretty much unavoidable during peak times, but tables get cleared the moment people leave, so turnover is really fast and the line never got too long 👍 Once the wait eased up a bit, the owner seated us — even as a party of two — at a bigger, more comfortable table, which showed some really thoughtful care for customers ❤️

What I liked about Kosi Isu Branch 😃

Everything on the table tasted good

The udon noodles were cooked just right and well-seasoned, and the fried items — tonkatsu, tenpura, croquettes — all had really thin batter that let the natural flavor of the ingredients shine through ❤️ It's not a famous spot near Isu Station for nothing, haha.

The dining room is big and comfortable

Even though it's a place with a wait near Isu Station, the restaurant is big enough that table turnover was really fast! Even with lots of customers inside, it never felt cramped or uncomfortable — it actually felt pleasant ✨️

The staff are very friendly

When it's this busy, staff can get tense or short with customers, but maybe because there were enough staff on hand, everyone was really friendly, and it was impressive to see them checking in to make sure customers weren't having any trouble 😇