What I especially like about Japanese restaurants (and what I believe to be a key to outstanding quality) is specialization. A great sushi bar serves only seafood. Even more specialized, an unagi restaurant sells only grilled eel, a tonkatsu restaurant only deep-fried breaded pork cutlets, and a gyūtan restaurant only beef tongue.

When I'm in Japan, I take my quest for specialization one step further by finding food that is typically unavailable at home. As an offal lover, that always means a meal or two of horumonyaki. Like yakitori, which has come to be known as any skewered meat but is technically grilled chicken, horumonyaki falls under the umbrella of yakiniku, or grilled meat. (This is admittedly confusing, as the Japanese think of yakiniku as Korean-style barbecue.)

Horumon (or motsu, to make matters even more confusing) means "the parts thrown away" and refers to pork and beef offal, which is grilled over binchotan charcoal and flavored simply with a tare sauce (generally soy sauce, sake, mirin, and sugar) or just salt. As you may have guessed, horumon also refers to hormone, derived from the Greek word hormon, which means to set in motion. Indeed, many Japanese believe that eating horumonyaki makes one genki (full of stamina).

I tried two types of horumonyaki restaurants during my latest trip to Tokyo. Saiseisakaba is a stand-up horumonyaki restaurant that makes you feel like a part of the lively Shinjuku district. You can stand at a counter in the window or at a table outside the doors and become part of the diverse street scene. Or, as I like to do, you can claim a spot at the counter and catch all the action at the charcoal grill.

Here you order items—like spleen, various stomachs, and small or large intestines—a la carte, and the chef passes them to you as they finish cooking. They're the perfect accompaniment to beer (my choice), shōchū (a Japanese distilled beverage) or sake. The setting is casual and friendly, full of drinkers. Ask for an English menu, but note that not everything translates well, and that they're sometimes out of some items (like the penis and "birth canal" that I tried to pair together).

In contrast to Saiseisakaba, Rukumatokyo is a more refined, sit-down place in the trendy Ebisu neighborhood. (There's also a branch in nearby Shibuya.) You can sit at tables with grills and vents, but the counter again lets you in on more of the action. Rukumatokyo doesn't have an English menu, but it's unnecessary if you order omakase. The chef will ask if you have any dietary restrictions, so just say "nandemo tabemasu" ("I eat everything") and leave it up to him, as he'll serve up many fascinating small plates (like a spoonful of raw pork liver and natto, as well as two parts of a pig brain with balsamic sauce) before giving you a tic-tac-toe board of offal to grill. (You can do it, or he'll lean over and grill everything to perfection for you.)

Check out the slideshow for a look inside both restaurants, including all of the interesting and amazing dishes I ate.

Saiseisakaba

3-7-3 Shinjuku, Marunaka Building, Tokyo 160-0022 (map) 03-3354-4829; ishii-world.jp/brand/motsu/nihonsaisei/shinjuku3

Rukumatokyo

2-3-5 Ebisu, Ishii Building, Tokyo 150-0021 (map) 03-3464-8929; facebook.com/rukuma.ebisu/info

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