Once upon a time, Japanese food was basically outlawed in Korea, a result of the Japanese colonization of Korea in the early part of the 20th century and its attempts to erase Korean culture. As a result, whether misguidedly or not, Japanese cultural aspects such as food and manga were hard to come by in Korea until the late 90's. The result was a wave of awful izakaya and/or easy-to-make every day Japanese food with little thought or effort put into it, just food as an attempt to catch the crest of a trend (otherwise known as the worst kind of food).
These days, however, 20 years on from the culture ban being lifted, there are a good number of restaurants striving to do Japanese food correctly. Jigudang is a small chain with a few locations around the city. The one near where I currently live in the north-central part of Seoul is a beautiful little space with dark green walls, sparse decor, yet with a welcoming atmosphere. The focus here is purely on the food, not the image.
I've eaten at Jigudang upwards of 20 times and have never been disappointed. They are only two things on the menu: gyu-don (beef over rice) and oyako-don ("mother and child" chicken and egg over rice). A restaurant with such a focused menu has no room for fault: their food must be on point or else there is no wiggle room. Also, such a small menu shows dedication to craft. The rice always has a nice, firm texture and the poached egg never, ever stays situated on top of the rice, always sliding down the side and away from the most perfect video clip. If you're ever up line 4 near Sungshin Women's University Station, seek out Jigudang/지구당 for a fantastic meal for under 10,000 won.
Jigudang - 6, Bomun-ro, 32-gil, Seongbuk-gu, Seoul
지구당 성북점 - 서울 성북구 보문로 32길 6