Every region of Japan has its own take on ramen, and Kyushu is the master of rich tonkotsu broth made from pork bones. The noodles tend to be straight, thin, and firmer than other styles.
Ajisen Ramen is a chain based in Kumamoto that has spread all over the world, including the US. Save your scorn for chain restaurants, because this is the real deal. I just wonder if the quality holds up outside of Japan.
I went twice during a long weekend in Kumamoto, once for the standard bowl and again for a bowl laced with mayu black sesame garlic oil. They have standard sides like gyoza and small rice bowls topped with flavorful pork bits. A card at the table advertises what I think were pig feet, another Kyushu thing, but I wasn't brave enough to gnaw on those.
As with most ramen shops in Japan, order at the vending machine and give your tickets to the server. This shop has a list of English and Chinese translations if the vending machine's pictures and kanji confuse you.