Cut the napa cabbage into quarters and remove the core.
In a large bowl, dissolve sea salt in water and soak the cabbage for 2 hours, turning occasionally.
Prepare the kimchi paste by mixing grated ginger, minced garlic, sugar, and gochugaru in a bowl.
Once the cabbage is wilted, rinse it thoroughly under cold water and drain well.
Combine the drained cabbage, radish, green onions, and kimchi paste.
Using your hands (wear gloves), mix everything together until the vegetables are coated.
Pack the mixture tightly into a clean jar, leaving some space at the top for expansion.
Seal the jar and let it ferment at room temperature for 1-5 days.
Taste daily until it reaches your preferred sourness, then refrigerate.
Enjoy your homemade kimchi as a side dish or ingredient in various recipes!