You should try Kofuku in Ansal Plaza. I personally love the Shoyu Ramen over here and apart from all this, they also have traditional Japanese style areas to offer you a great dining experience.
Yum yum cha in Khan market does authentic Japanese dishes including ramen, sushi , dimsums etc.
Majnu ka Tila area is your best bet! Busan Korean Restaurant.
There is this Fuzi restaurant in Cp if you haven't checked out!