R O.
Yelp
A very rich and assertive tonkotsu ramen that I can recommend wholeheartedly.
Itto-ka is a small local chain with 3 stores in Akihabara, Kayabacho, and Akasaka, the original location. It serves Yokohama-style Tonkotsu based ramens, that are characterized by a rich tonkotsu (pork-bone) based white broth that is heavily seasoned with soy sauce, that are often eaten together with a bowl of rice.
Itto-ka offers several variations of Ramen, but I have only tried their basic 700-yen ramen, and their Itto-mori 970 yen ramen. The 970 yen version is the same basic ramen, but comes topped with extra green onion, nori, egg, and extra-thick cut boiled pork.
The noodles are fairly thick almost udon type noodles. They have great texture and are great paired with the very flavorful white broth soup. The soup is very rich and salty--I recommend against getting extra tare-sauce in your soup, as it would almost certainly be overdoing it. It has a very assertive pork based flavor, without use of seafood ingredients--I suspect a solely vegetable and meat based composition (though I can't be sure).
The pork on the Itto-mori version deserves special mention. Normally, most ramen stores serve a relatively thin sliced piece of pork as an accent to the dish. Itto-ka's bonus-pork version doesn't increase the number of slices of pork, but dramatically increases its' thickness--rather than a paper thin slice of pork, you get a piece of pork that is a full half inch thick or more. The pork loin has been boiled in a flavorful broth long enough it is very tender and comes apart easily in your mouth.
Service is relatively quick, and as an added bonus, if you finish your entire bowl (noodles, topping, and soup), your bowl reveals a 完食 (Kanshoku - completely eaten) kanji at the bottom of the bowl--an attendant will give you a Kanshoku coupon that entitles you to a free bowl of rice, extra noodles, extra nori, or extra egg on your next visit.