1.Slice tuna as thinly as possible; place, in single layer, on large platter, drizzle with vinegar. Cover; refrigerate until required.
2.Meanwhile, grate peeled daikon finely. Place daikon and chilli in fine sieve set over small bowl; stir with small wooden spoon to combine then press with back of spoon to extract as much daikon liquid as possible.
3.Drain vinegar from tuna. Divide tuna among serving plates; drizzle with combined mirin and oil; sprinkle with seeds. Serve tuna with red-maple radish and seaweed.