Umeboshi, pickled plums, is one of the Japanese traditional daily side dishes. Speaking of Umeboshi, the taste has been just salty and sour until recently since it was originally a preserved food with high concentrated salt. It can be kept under room temperature for longer than years. Furthermore, its antibacterial function, which reduces the risk of food poisoning, is useful for us to make a lunch box such as Onigiri, a rice ball, with Umeboshi at the center.
Along with the wide availability of fridges, Umeboshi isn't necessarily to be kept under room temperature anymore. Which means, the high concentrated salt isn't needed to be the preserved food. And it has expanded to have more variety of seasonings such as sweet flavor by marinating with honey. Like other flavors, Bonito or Konbu soup stocks are used for these seasonings as well. These are amazingly delicious comparing with salty and sour only taste ones, I think. But unfortunately, the price of new tasty flavors is getting higher, like 10 times more expensive than the traditional ones at the highest.
In the past, it used to hold the role only as preserved food, but it now has established additional new positions as a luxury gift or a souvenir. If you have a chance to visit Japan once the COVID-19 pandemic is over, I recommend you to try various flavors of them! And someone says that Umeboshi is Japan's secret for longevity, though I'm not sure if it's true but I guess it's worth a try!