Cut the Napa cabbage in half lengthwise and then cut each half into thirds.
Place the cabbage pieces in a large bowl and sprinkle with sea salt. Toss to coat evenly.
Add enough cold water to cover the cabbage. Let it sit for 1-2 hours, tossing occasionally to ensure even salting.
After 1-2 hours, rinse the salted cabbage thoroughly under cold water to remove excess salt.
Drain well and squeeze out as much water as possible.
In a bowl, combine grated ginger, minced garlic, sugar, fish sauce (or soy sauce), and Korean red pepper flakes.
Mix well to form a paste.
In a large mixing bowl, combine the drained cabbage, carrot, green onions, and daikon radish (if using).
Add the kimchi paste to the vegetables and toss thoroughly to coat everything evenly.
Pack the kimchi mixture tightly into a clean jar or container, pressing down to remove air bubbles.
Leave some space at the top to allow for expansion as the kimchi ferments.
Seal the jar or container with a lid. Let it sit at room temperature for 1-2 days to start the fermentation process.
After 1-2 days, move the kimchi to the refrigerator. It will continue to ferment slowly and develop more flavor over time.
Enjoy your meal!