Japanese food traditionally includes a lot of tsukemono (漬け物), or pickles. The first thing most Americans will think of when you say pickles is dill (cucumber) pickles that go with sandwiches; however, pickles are any vegetable that has been preserved with brining. Japanese pickles cover a wide range of base ingredients, including carrots, cucumbers, ginger, and plums; as well as a wide variety of pickling styles: salt, miso, vinegar, nuka (rice bran), and more. Some recipes call for the pickling mixture and vegetables (or fruit) to be aged overnight or for several months, but this recipe can be consumed right after cooking!
Aka-zuiki (赤ずいき) are another Kaga Yasai (加賀野菜, Kaga-region heirloom vegetables) and are in season from mid-June throughout September. Zuiki is the stem of the taro plant (satoimo, 里芋), a slimy potato featured in Japanese cuisine; Americans might know taro as a flavoring of Asian desserts, especially in bubble tea (boba). Aka-zuiki just means red zuiki, and the stem has a reddish color which is enhanced by vinegar.