"If you can't find daikon radishes, use a bunch of small red radishes when in season. I love this stir-fry because you can add any veggies you like, including spring onions, savoy, or Chinese cabbage... whatever you have handy."
Combine daikon radish, soy sauce, sake, sesame oil, ginger, garlic, and mirin in a large bowl. Add sliced pork; let marinate for 5 minutes.
Heat vegetable oil in a wok or large skillet over medium heat. Add onion; cook and stir until softened, 3 to 5 minutes. Remove pork from marinade and add to the wok; cook and stir until evenly browned, 3 to 5 minutes. Pour in remaining marinade; cover and cook until bubbling, about 5 minutes. Season with salt and black pepper.