Stir together the tamari, mirin, water, rice vinegar, and grated ginger in a small bowl. Set the dipping sauce aside.
Pat the shrimp very dry with paper towels. Make a few shallow cuts along the underside of each shrimp to prevent curling, then lightly dust all the shrimp with a thin coat of rice flour taken from the measured amount, shaking off the excess.
Heat about 2 inches of avocado oil in a large heavy pot or Dutch oven over medium-high heat until it reaches 375°F.
While the oil heats, make the batter. In a bowl, whisk together the remaining rice flour, cornstarch, tapioca starch, salt, and baking soda. Add the ice cold club soda and cold egg and stir very briefly with chopsticks or a fork just until barely combined. The batter should be lumpy and thin - do not overmix.
Holding each shrimp by the tail, dip it into the cold batter, letting the excess drip off for a second. Carefully lower it into the hot oil. Fry 4 to 5 shrimp at a time for 2 to 3 minutes, until the coating is very light golden and crisp.
Transfer the shrimp to a wire rack and repeat with the remaining shrimp.
Serve the tempura shrimp immediately while still hot and crispy, alongside the dipping sauce.