Wash the perilla leaves thoroughly and drain the excess water.
Thinly slice the onion.
Mix soy sauce, water, sugar, vinegar, minced garlic, and spicy chili pepper to make the pickling sauce.
Layer the perilla leaves, onion, and spicy chili pepper in a container.
Pour the prepared pickling sauce over the ingredients and let it mature in the refrigerator for at least one day.