1Trim the greens and root ends from the radishes. Gently smash each radish with a meat mallet (or the side of a knife) until it cracks but stays mostly intact. Place in a bowl, sprinkle with 1 Tbsp kosher salt, and toss to coat. Let sit for 30 minutes to draw out moisture.
2Rinse and drain well, then transfer the radishes to a large glass jar with a lid.
3In a small pot, combine the rice vinegar, water, sugar, soy sauce, garlic, sriracha, sesame oil, white pepper, and remaining 1 tsp kosher salt. Bring to a simmer over medium-high heat, stirring until the sugar dissolves. Remove from the heat and let cool slightly.
4Pour the brine over the radishes, cover, and refrigerate overnight.