Cut daikon into 1 1/2 inch thick rounds. Peel. Bevel edges of each slice to prevent the edges of the daikon from breaking up while cooking. Cut a shallow cross into one side of each slice to facilitate cooking.
In a saucepan, arrange each slice cross-cut side down. Cover with rice water and cook until tender; drain.
Combine simmering sauce ingredients.
Place cooked daikon on top of the kombu in a saucepan. Pour simmering sauce over and bring just to a simmer, then reduce heat to low and simmer until soft, about 20 minutes.
Arrange daikon slices in 4 warmed dishes. Discard konbu. Pour remaining cooking liquid over daikon and serve.