Rokugo is inside the Thinkpark office/shopping complex just west of JR Osaki station, on the opposite side as Osaki New Gate City. Thinkpark is another one of these large shopping complexes that never seems to have anyone in it. However it does have two British pubs and a artificial soccer turf outside in front that some teams were playing on today. Rokugo is nestled in the back on the first floor near the escalators. They have some interesting and different dishes that caught my eye. First of all, their main line of hot ramen dishes is actually "beef bone based", also known as gyu-kotsu (as opposed to ton-kotsu, pork-bone-based). This is a rarity in Tokyo. The ramen had Hakata-style thin whitish noodles in it just like Hakata tonkotsu, and it also have roast-beef-like slices of beef, which were pretty good. Portion was a bit small so I recommend you get the chashu topping (they call it chashu but it is actually beef) and the omori size for the noodles for a total of 1200 yen. It had a lot of chopped negis and menmas in it. The broth had a good beef and shoyu flavor (you can also get it in miso and shio). This would be a good place to bring someone who wants to try ramen in Tokyo but does not eat pork (but can eat beef). Also, they have a lot of other types of things including shabu shabu, yakitori, etc. Seems to be a general restaurant that also happens to have some good ramen. They also have as a limited time special, a "ratatouille" tsukemen with chopped tomatoes, onions and eggplant in the dipping sauce. That's certainly different - very creative.
Ikemen Blog (more pictures)
Diddlefinger Map (English labels)