Wash, peel, and thinly slice the lotus root into a half moon shape. Place the sliced lotus root into a bowl or pot of water with the vinegar. Keep the lotus root slices soaked until ready for use.
Wash and slice the snow peas in half diagonally, forming a spear shape.
Heat a large wok or frying pan over high heat and add the sesame oil.
While the wok is heating, drain the lotus root and pat dry with a kitchen towel or paper towels. (Removing the moisture helps keep the stir fry crispy and prevents oil splattering).
When the oil is just starting to smoke, add in lotus root, snow peas and chili flakes.
Stir fry over high heat for 3-4 minutes, until the lotus root begins to turn slightly translucent.
Add in the soy sauce, mirin, and sake. Toss the stir fry quickly to coat the lotus root and snow peas, about another 1-2 minutes.
Once the soy sauce mixture begins to caramelize and smell slightly smoky, remove the stir fry some the heat and turn the stir fry out onto a serving platter. Serve immediately.