Onigiri a good alternative to pre and post race snack.
Onigiri is essentially a rice ball, made from white rice and often wrapped in Nori seaweed. Rice is filled with pickled vegetable or any other salty or sour ingredient.
Perfect combination of carbohydrates and proteins.
Could be also used during long running or ultramarathons.
A glass of salty miso soup will match it perfectly
The country offer generally a lot of other interesting options, Japan is an interesting country for streetfood.
Here a list of streetfood as a good alternative for a post training:
Nikumaki onigiri: is a rice ball wrapped with thinly sliced beef and cooked in sweet soy sauce.
Dango, mochi dumpling: Served on a skewer, these round dumplings are made from rice flour and water and boiled until firm
Imo mochi (Potato rice cake): It is made by adding potato starch to steamed and crushed potatoes, kneading well, shaping into dumplings, and baking until brown. It is eaten with sweet and seasoned soy sauce, butter and sugar.
Yaki soba: Wheat noodles, pork, cabbage, and onions are fried on a griddle, then topped with benishoga, katsuobushi, aonori, a squeeze of Worcestershire sauce, Japanese mayonnaise, and occasionally, a fried egg
Yakitori: chicken skewers that are grilled over charcoal and can be found all over Japan. Yakitori is made from all parts of the chicken, such as the thigh meat, tail meat, and even the skin, each with their own unique flavor. The most common seasonings are tare (soy grilling sauce) and shio (salt), but wasabi, umeboshi (sour pickled plum paste), and karashi (Japanese mustard)
Takoyaki: are golden balls of fried batter filled with little pieces of octopus, tenkasu (tempura scraps), benishoga (pickled ginger) and spring onion.
Okonomiyaki: is essentially a savoury pancake packed with cabbage, egg, seafood and noodles.
Ikayaki: Fresh, tender squid is grilled over charcoal, given a generous coating of shoyu (soy sauce) and served with a slice of lemon or lime.
Yakiimo: Satsuma-imo (a type of Japanese sweet potato) are baked over a wood fire and served in brown paper packets.
Yaki Tomorokoshi: char-grilled whole cobs of corn brushed with a glaze of soy sauce, mirin, and butter, which give the corn a sweet, savory and creamy depth
Imagawayaki: A thick pancake like dish filled with red bean paste, meat, potatoes, curry, cheese or custard
Kare Pan: breads filled with different kinds of savory ingredients. Made of slightly sweet dough that has been breaded and deep fried, a kare pan has rich Japanese curry at its center.
Taiyaki: a fish-shape cake/snack filled with azuki sweet red bean paste.
Dorayaki: dessert with red bean filling between two slices of sweet fluffy pancakes