Umeshu and Umeboshi
When you are supermarkets, you must have seen a bunch of bottles and suger on sale these days. Yes, this time around the year is the time to make your own Umeshu and Umeboshi at home in Japan.
Umeshu （梅酒） is a Japanese liqueur made from ume fruits (while still unripe and green) in alcohol and sugar. It has a sweet and sour taste. I have quite a few friend who normally do not drink alcohol but like to drink Umeshu. Homemade umeshu's main ingredients are ume fruits, sugar and shochu. Japanese restaurants serve many different varieties of umeshu and also make cocktails. There are some Izakaya restaurants specialized in Umeshu too.
Some people also make homemade Umeboshi. Ume fruits are picked in salt and they will be colored by perilla herb. I love umeboshi, but I don't really like the overly salty ones. They range in salty/sweetness, and I always get the "low sodium" ones which taste slightly sweeter. They are popular as a filling for rice ball and you can also eat it with plain rice!
Both Umeshu and Umeboshi are Japanese traditional foods and I hope you can enjoy both while you are in Japan!