When life gives you sour oranges, make ponzu sauce.
Ponzu is such a versatile condiment and its acidity adds a lot more dimension than regular soy sauce. It's also extremely easy to make your own ponzu at home. Especially when you find sour oranges (called dai-dai in Japan, and sometimes called "bitter orange" here in the States), you should make your own batch of ponzu. You can also use other citrus, such as meyer lemon, yuzu, kabosu or sudachi, if you have access to a bunch of it. Though I haven't done it, meyer lemon would make a really nice ponzu, with its awesome sour/bitter/sweet flavors.
Anyhow, here is how to make your own ponzu.
These are sour oranges. They're more bland than sour.
I bought eight of them, and you can get more or less.
Squeeze juice. You see one different colored orange on top middle, which is meyer lemon. I had one in the fridge, and squeezed it as well. Why? Just because it was there.
You may think the skin is hard but it's pretty soft and easy to squeeze.
Now, strain the juice and measure. I had 600ml of juice.
Recipe is something like: equal parts of soy sauce and citrus juice, 10% each of mirin and sake, plus flavorings. The proportions can be modified. Some people use more sake, some people use vinegar on top of citrus. Be creative.
Add the same amount of soy sauce of your choice, plus mirin and sake -- if you have 600 ml of juice, use 60ml each of mirin and sake. Then add flavors. I added 2 pieces of kombu, 3 dried shiitake mushrooms, and 2 big handful of bonito flakes.
Put this in cool place for about a week. In a day or two, everything will sink to the bottom. After a week or so, strain and taste. If the ponzu is too sour, add a bit of mirin to your liking. You can be creative about what you do with the strained solids, maybe make some tsukudani?
Use this ponzu as a salad dressing or dipping sauce. You may think it would be really pungent since it uses real citrus -- but it's actually a lot softer than store-bought ponzu. Plus, you get all the good juice from the shiitake/kombu/bonito which adds a lot of flavors as well. It's also great that there's no preservatives/additives when you make things on your own.