Takoyaki: octopus, ball-shaped, and everywhere
Takoyaki is widely credited to Osaka in the 1930s: bite-sized balls of a wheat-flour batter, each with a piece of octopus at the centre, cooked in a special pan of hemispherical moulds and flipped with picks until the outside crisps and the inside stays soft. They're finished with a thick sweet-savoury sauce, mayonnaise, dried bonito flakes and often green nori.
Street stalls around Dotonbori sell them by the six or eight-piece tray, and quality varies a lot — a queue at a stall is usually the best signal that it's worth trying.
Okonomiyaki: Osaka-style, mixed not layered
Okonomiyaki is a savoury pancake built from a batter of flour, egg, shredded cabbage and a protein of your choice, cooked on a griddle and finished with the same family of sauce, mayonnaise and bonito flakes as takoyaki. The Osaka style mixes everything into the batter before cooking, which is the key difference from Hiroshima-style okonomiyaki, where the ingredients are layered rather than mixed.
How to order and eat
Many okonomiyaki restaurants cook the dish at your table on a built-in griddle, and some hand you the spatula to finish it yourself — don't be afraid to ask staff to demonstrate first if it's your first time. Takoyaki, by contrast, is almost always sold ready-made and eaten standing or walking.
The name okonomiyaki roughly translates to 'grilled as you like it' — most restaurants offer a long list of protein and topping variations, so it's a reasonable dish to order even for picky eaters.