1 15 centimeter piece daikon, peeled, cut into matchsticks
1 cup shredded carrots
Toasted sesame seeds and cilantro with tender stems (for serving)
Remove dark green tops from scallions and thinly slice; set aside. Blend scallion bulbs, kimchi, vinegar, Sriracha, fish sauce, and sesame oil in a blender until smooth. With motor running, very slowly stream in vegetable oil; blend until dressing is thick and airy. Add a tablespoon or two of water if dressing is too thick. Set aside.
Tear off leaves from Napa cabbage until you get down to the crunchy white part. Rip outer leaves into six centimeter pieces. Thinly slice core crosswise until you have about three cups; reserve remaining cabbage for another use. Core and thinly slice purple cabbage. Toss in a large bowl with daikon, carrots, and reserved scallion tops. Season with salt; pour reserved dressing over. Toss to coat, transfer to a platter, and top with sesame seeds and cilantro.