It seems possible that I was the only person to start the day with yogurt and sudachi for breakfast. Despite the 20 or more different kinds of homemade marmalade in the house, that's the admittedly unexciting task to which I tend to assign them.
The sudachi is a Japanese citrus fruit which is likely a hybrid of the mandarin and the papeda subgenus, making it a relative of the yuzu and the kaffir lime. It's fairly lime-like, the flavor of the juice sharper and less complex (or "more focused" if you like) than that of the yuzu, the rind less perfumed than the kaffir.
You can occasionally find bottles of sudachi juice. You may be able to find the fresh fruit at the farmers' markets of citrus-growing parts of the country, or stores with an especially good selection of Japanese produce. I bought mine from the White Dove Passion Fruit Farm, so they weren't cheap thanks to the shipping -- but on the other hand, they came out to about a dollar each, and even navel oranges cost nearly that much at my supermarket. You know how I am: I hadn't had them before, so didn't really have a choice.
I have a mental list of things to try, with any citrus I pick up that you can't just eat. I mean, there are a million things you can do with citrus, but if you're trying something new, you want to try it in something where it's the most prominent flavor.
Things to do with citrus that's too sour to eat out of hand:
Cocktails: Aviation, Whiskey Sour, Margarita
"Key lime" pie
Shaker "lemon" pie (if you think the rind is palatable enough)
Liqueur: straight (vodka + peel), sweetened (vodka + peel + sugar), bitters (vodka + peel + botanicals + bittering agent such as gentian, cinchona, grapefruit pith, etc), infused spirit (Seville orange + gin is traditional)
Flavored sugar (zest + sugar + time)
"Lemon"ade, lemonade iced tea
Mojo criollo (juice + olive oil + garlic + Cuban oregano, use as dip for fried yuca, fish, etc)
I also tend to dry a lot of the zest, and freeze a lot of the juice.
With the sudachi, I made a sudachi cream pie, two flavored sugars (one with yuzu and sudachi, one with Seville orange and sudachi), a quart of marmalade to have with yogurt, and am left with a cup of juice -- some of which I think I'll use for mojo criollo.