Gyoza are similar to Chinese potstickers, but tend to be made with a thinner wrapper and are slightly smaller.
Combine pork, cabbage, Chinese chives, shiitake, ginger, garlic, 1 tsp. of the sesame oil, soy sauce, salt, sake, and black pepper in a large bowl. Mix well, kneading until fully incorporated and very sticky.
Place a teaspoon full of the filling in the center of a wrapper. Dampen the outer 1/4" of the wrapper with water. Fold the wrapper in half over the filling. Working from one side towards the center of the gyoza, make a pleat every 1/4" until reaching the center. Continue pleating working form the other side. Press pleats to ensure a seal.
Heat the oil in a large pan over medium heat. Place the gyoza in a single layer, flat side down, in a circular pattern around the pan. Fry until the bottoms are golden brown.
Add the water to the pan, and immediately cover with a lid. Steam gyoza until most of the water has evaporated.
Remove lid and continue to cook until the bottoms are crisp again. Serve with dipping sauce.