Start by preparing the marinade. In a pot, combine soy sauce, water, soju, mirin, plum syrup, sugar, dried kelp, onion, apple, scallions, garlic, ginger, cheongyang pepper, dried pepper, and peppercorns. Bring to a boil over medium heat then reduce to a simmer. Simmer for 10 minutes then strain. Transfer to the fridge to cool completely.
Next, prep the shrimp. If shrimp is still frozen, soak it in a bowl with 4 cups of water and 1 tablespoon of salt for 30 minutes or until defrosted. If your shrimp is already defrosted and thawed, skip this step.
Using a pair of sheers, cut the pointy areas of the head, whiskers, and legs. Carefully remove the shell from the body of the shrimp. The tail can be left on or taken off - it's your preference!
Next, devein the shrimp with the toothpick. Repeat until all shrimp is cleaned. Transfer the shrimp to a shallow plate. Add 1/2 cup soju and soak for 10 to 15 minutes. Rinse under cold water then strain well.
Transfer the shrimp to a clean glass container. Top with onions, cheongyang pepper, red pepper, and lemon slices. Pour the chilled marinade on top of the shrimp. Cover with an airtight lid then place in the fridge for at least 24 hours or up to 48 hours.
Serve with a bowl of rice and enjoy!