The Difference: Okonomiyaki Sauce vs. Tonkatsu Sauce
As for the brown sauce, in addition to Tonkatsu sauce, Worcester sauce, and Chuno sauce, we commonly use Okonomiyaki sauce at home.
As I wrote in this article, the first three sauces are similar in taste and can be used interchangeably to your preference.
Okonomiyaki Sauce vs. Tonkatsu Sauce

However, Okonomiyaki sauce is somewhat different from Tonkatsu sauce, Worcester sauce, and Chuno sauce, though they all look alike.
For example, when I compare Tonkatsu sauce and Okonomiyaki sauce, the primary difference is as follows.
Tonkatsu (豚カツ)
As its name suggests, Tonkatsu sauce (とんかつソース) matches best with the Japanese-style pork cutlet Tonkatsu.
Meanwhile, Okonomiyaki sauce (お好み焼きソース), also known as Okonomi sauce (お好みソース), is the brown sauce primarily meant for Okonomiyaki.
Okonomiyaki (お好み焼き)
Okonomiyaki is a savory Japanese pancake whose flour dough comes with various ingredients, such as vegetables, pork belly slices, and seafood.
As with Tonkatsu, Okonomiyaki is popular comfort food in Japan.
Product Brand

When we Japanese think of Okonomiyaki sauce, many probably picture Otafuku (オタフク)’s Okonomi sauce.
Meanwhile, the Tonkatsu sauce most familiar to us is arguably Bull-Dog (ブルドック)’s Tonkatsu sauce.
Ingredients

In terms of ingredients, the Bull-Dog Tonkatsu sauce I have on hand consists of
|
Fruit (Tomato, Apple, Prune, Lemon, Carrot, Onion), Brewed vinegar, Sugars (High fructose corn syrup, Sugar), Salt, Starch, Yeast extract (including Soybean), Spice |

On the other hand, the Otafuku Okonomiyaki sauce consists of
|
Vegetables & Fruit (Tomato, Dates, Onion, and so on), Sugars (High fructose corn syrup, Sugar), Brewed vinegar, Hydrolyzed vegetable protein, Salt, Alcohol, Soy sauce, Spice, Oyster extract, Meat extract, Yeast extract, Kombu seaweed, Protein hydrolyzate, Shiitake mushroom, Thickeners (Modified starch, Polysaccharide thickener), Seasoning (including Amino acid), Caramel pigment (Partially including Wheat, Soybean, Chicken, Pork, Peach, and Apple) |
Taste

Taste-wise, in a word, Tonkatsu sauce is a thick, umami-rich version of Japanese Worcester sauce. It is sweetish and moderately spicy.

Compared to Tonkatsu sauce, Okonomiyaki sauce has a slightly thicker consistency and a more gentle fruity flavor with almost no spiciness.
Uses
Yakisoba (焼きそば)
In addition to the Tonkatsu pork cutlet, many Japanese people like to eat shredded cabbage with Tonkatsu sauce.
We also commonly use the thick, flavorful brown sauce to season Yakisoba noodles.
Takoyaki (たこ焼き)
Okonomiyaki sauce not only goes perfectly on Okonomiyaki pancake and Takoyaki (たこ焼き) octopus balls, but it also pairs well with noodle dishes, such as Yakisoba and Yaki Udon.
Additionally, some Japanese home cooks like to use Okonomiyaki sauce as a secret seasoning in curry.

