The sign of a good onigiri is one that has been made by hand but is not packed too hard.

While onigiri may seem simple, there are many variations, starting with the rice. Depending on what kind is used, the flavor, aroma and texture changes for white rice, while genmai (un-milled brown rice) offers earthy, nutty notes. Rice may be cooked with a variety of grains and seeds, called zakkokumai, which often changes the color to a lavender blush, while adding both nutrients and a rich texture.

Fillings can be from the sea or land, but depending on what is added the flavor can alter: roe offers bursts of salt and umami, pickled vegetables or grilled salmon provide a crunchy texture, and tori soboro, ground chicken simmered in sweet soy sauce, is a meaty variety.

Vegetarians have options that include konbu, kelp cooked in a sweet soy broth, pickled greens, such as takana or nozawana, pickled umeboshi or nattō (fermented soybeans).

Most of the onigiri shops in the city are for take-away and can be found near busy stations, but some shops have sitting areas.

Inside Tokyo Station’s Yaesu Central Gate, Honnoriya has a perpetual line outside it in the mornings. In Aoyama, Omusubi Gonbei has a nice selection of brown rice onigiri. Omusubi no GABA in Akihabara is the only shop I could find that serves germinated rice balls, which are more nutritious.

For a special treat, make the journey to Risaku in Tokyo’s Yanaka neighborhood, near Sendagi Station. It’s not a chain store like the others; the miso for the grilled onigiri is rich with mushrooms that are sauteed with garlic before being added to the soup. The curious cream cheese and tarako (salt-cured pollack roe) combination was so good I made it at home.

Honnoriya Tokyo Station inside Yaesu Central Exit, 1-9-1 Marunouchi, Chiyoda-ku, Tokyo; 050-3797-3181; opens 7 a.m.; www.jefb.co.jp/honnoriya. Omusubi Gonbei 1-7-3 Shibuya, Shibuya-ku, Tokyo; 03-3498-2556; opens 8 a.m., weekdays, 9 a.m. weekends and holidays; www.omusubi-gonbei.com/shoplist/tokyo/shibuya/aoyama.html. Sendagi Risaku 2-31-6 Sendagi, Bunkyo-ku, Tokyo; 03-5384-7292; opens 8 a.m.; www.risaku.jimdo.com. Omusubi no GABA 4-7-2 Soto Kanda, Chiyoda-ku, Tokyo; 03-5298-5567; opens for take-away 7 a.m. weekdays, 10 a.m. weekends and holidays, eat-in starts at 11 a.m.; www.satake-japan.co.jp/ja/about/omusubi.html.