Shrimp with Pickled Radishes

Name: Shrimp with Pickled Radishes
Ingredients: 6 red radishes, trimmed, thinly sliced; ¾ cup white wine vinegar; 3 tablespoons sugar; 1 teaspoon crushed red pepper flakes; 2 teaspoons kosher salt, divided, plus more; 1½ cups short-grain sushi rice; 1 tablespoon dried hijiki (seaweed); 1½ pounds large shrimp, peeled, deveined; 1 medium shallot, finely chopped; ¼ cup soy sauce; 1 tablespoon plus 2 teaspoons gochujang (Korean hot pepper paste); 4 teaspoons unseasoned rice vinegar; 1 tablespoon fish sauce; 2 teaspoons honey; 1 teaspoon toasted sesame oil; 2 cups baby mizuna or arugula; 2 teaspoons toasted sesame seeds; Gochujang can be found at Korean markets and online.