Ichiryuan, located at the basement of Hokuren Building. We tried their highly recommended Miso Noodle with Roast Pork (1,000Yen for a small one). The chashu is one of the best I had but noodles honestly were pretty alright. The soup base is made with ingredients sourced specially from Hokkaido and have been their popular dish for the past 8 years.
According to @the_ivyvines it is polite to slurp your noodles, not that I don't find it nice but I didn't want to dirty my white top. 😁