Kumamoto ramen takes the regional tonkotsu pork bone soup as its starting point and often adds a little chicken stock, thicker noodles compared to the north's Hakata, and—last but not least—heaps of garlic, be that mayu garlic oil, fried garlic or powdered garlic.
Tengaiten (天外天) typically draws a strong crowd and might serve as the best example of local Kumamoto-style ramen in the castle district area. With a number of famous shops closing doors early (at 8pm), Tengaiten's relatively easy accessibility certain adds to its appeal, even if its location (in a predominantly nightlife area) draws a fair number of late-night revellers.
Tengaiten serves 3 different kinds of bowl: the basic ramen (¥700), a spicy ramen (¥750) and char siu ramen (¥1,000). As you're ushered into a vacant spot along the 12-seat counter between other late-night revellers, orders are placed directly from the menu to staff and paid for at the end (i.e. no ticket machines). The basic ramen is perhaps the best choice here for first-timers, with an impressive quantity of pork included anyway and giving you the most authentic Kumamoto-style experience.
Tengaiten ramen is classic Kumamoto style. The tonkotsu soup is full of flavour but of the assari kind – not as heavy or rich as other tonkotsu styles, thanks to the chicken stock blend. Along with the char siu pork and noodles, scallions, kikurage mushrooms and garlic complete the bowl. The garlic here is a mixture of fried garlic chips, garlic powder and mayu black/burnt garlic oil. You can even add sliced garlic on the side if you feel adventurous.
Tengaiten is a 2 minute walk to the south of Suidocho station, on the Kumamoto City Tram line.