Mixed katsu set with giant shrimp tempura and mini udon: Kosi Seongsu

I visited Kosi Seongsu Branch, which has been building a word-of-mouth reputation in the alleys of Seongsu-dong for its authentic handmade Sanuki udon and crispy Japanese tonkatsu.

Exterior and cozy interior

Set on the first floor of a brick building, the restaurant gives off a warm, comfortable Japanese-dining vibe right from the entrance, with warm wood tones and soft lighting.

The signboard outside neatly lists the signature dishes — ten bukkake udon, mazeudon, mixed katsu — with photos, which really gets the appetite going before you even step in.

Inside, it's tidy and clean, mainly wood tables, with a comfortable mix of seating for two up to four people!

Every table has a contactless tablet ordering system, so you can browse menu photos and order right from your seat, haha.

On the side of each table there's a sesame grinder and salad dressing you can add to taste, which is nice and convenient.

Bukkake udon set (chicken karaage & inari sushi)

To really put this Sanuki udon specialist's skills to the test, I ordered the bukkake udon, a refreshing cold udon eaten mixed together.

Being handmade noodles, they're coiled into a pretty spiral shape, and even at a glance you can see the glossy sheen.

They feel as if just rinsed in ice-cold water — bouncy and firm, with that distinctive heavy, chewy Sanuki texture on every bite.

I poured the tsuyu from the little gourd-shaped pot evenly over the noodles, piled on scallions, grated radish and crispy tempura bits, then squeezed a bit of lemon juice and mixed it all together — the result is a savory yet refreshing umami that fills your whole mouth...!!

The set comes with three big, crispy boneless chicken karaage pieces that pair well with the noodles, plus generous sweet-savory braised inari sushi and cabbage salad — a filling spread on its own.

The ultimate in crispiness! Mixed katsu set

This is the mixed katsu set, where you can taste crispy breading and juicy meat at the same time.

The loin cutlet in its golden breading is crisp on the outside and, on the inside,

holds moist juices, chewing soft with no off flavor.

The giant shrimp tempura, fried whole from head to tail (I'm guessing black tiger shrimp...?), felt

noticeably heavy when I picked it up with chopsticks, the flesh so plump and full — dipping it in tartar sauce was such a treat, haha.

A warm, deep bonito-broth mini udon comes included with the set as standard, cutting through the richness of the fried dishes nicely.

Fluffy white rice sprinkled with furikake seasoning is served too, so

you can clean the plate right down to the last bite.

To sum up

If you want to properly experience the charm of freshly made, chewy handmade udon noodles in Seongsu-dong, this is a place you won't regret. The refreshing chewiness of the bukkake udon and the hearty crispiness of the mixed katsu balance each other beautifully for a satisfying, filling meal.

Thanks to the neat plating and cozy space, it works just as well for a date as it does for eating alone — no pressure either way. What stood out most was how the noodles kept their bounce and the tempura kept its crunch all the way through the meal.

From the basic side dishes to the extras, you can tell real care went in, and you get the depth of authentic Japanese noodle cooking at a reasonable price — a genuinely great restaurant I'd happily revisit in Seongsu-dong.