So far this is the best suratanmen in Tokyo, in my opinion, and this place has the awards and plaudits to prove it. Ryuzan (dragon mountain?) is out east in Koto-ku on the Toei Shinjuku line. Definitely better suratanmen/sanratanmen (酸辣湯麺) than Youshuu Shonin. Too bad it's a bit far from the loop, but the good news is that you can just walk about 3 minutes from Yodobashi Akiba in Akihabara over the river to Iwamotocho station on the Toei Shinjuku line. This place is right smack in the middle of a residential neighboorhood, any place else in the world like this would look quite out of place. They have an extensive menu of Chinese dishes, with many spicy ones including kuro goma dan-dan men. Pictures are above. At 1 PM on a Saturday there were relatively few people in there. Their sanratanmen ("hot and sour soup" with noodles) has been written up in numerous Tokyo magazines including Tokyo Walker, Ramen Walker, etc. - pictures of their articles ring the walls of the place inside and out. The omori sanratanmen was a huge portion of peppery spicy vinegary goodness. The ingredients were combined in perfect proportions. The vinegar taste was there but not too strong, and the pork and egg were generously apportioned too. They will anticipate the inevitable and deliver a picture of water to your table if you order the sanratanmen. If you like sanratanmen you must go there - no if's, and's or but's.
Diddlefinger Map (English labels)