Put the plum on the cutting board and wack the top with a hammer. The pit will be separated from the fruit. Discard the seeds and collect the fruit.
In a large airtight container, layer 1/3 of the plum on the bottom and sprinkle 1/3 of the sugar. Repeat the layering until the sugar covers the top. Close the lid and store in a dark place. Let them ferment for 3 month.
When ready, strain the plum and syrup in a fine strainer. Collect the syrup into a jar and store in a fridge.
For the use of fermented fruit, rinse lightly with water once, then season with Korean chili paste, chili flakes, red onion, garlic, sesame oil, and sesame seeds. Toss well to coat.