Place the butter, miso, and togarashi in a small bowl and mash with the back of a spoon until evenly combined; set aside. Cut the leafy tops from the radishes. Coarsely chop, wash, and dry the tops; set them aside. Wash the radishes, trim the stem ends, and halve them (quarter them if they’re large) and set aside. Heat the oil in a large frying pan over medium-high heat until shimmering. Add the radishes and arrange them cut-side down in a single layer. Season with salt and sear until golden brown, about 4 to 5 minutes. Flip and cook the other side until golden brown and the radishes are crisp-tender, about 3 to 5 minutes more. Reduce the heat to medium. Add the radish tops, 1 tablespoon of the water, and salt to taste. Cook, tossing occasionally with tongs, until the tops are completely wilted, about 2 minutes. Remove the pan from the heat. Add the butter-miso mixture and the remaining tablespoon of water and stir until the butter-miso mixture melts and coats the radishes and radish tops. Add the vinegar and stir to combine. Taste and season with salt as needed.