Place all ingredients in a large bowl. Using clean hands, toss the daikon until all the ingredients are evenly dispersed and the daikon starts to release liquid. Let stand at room temperature for at least 1 hour.
For the Steak
Pat the steak dry with paper towel and set aside.
In a small bowl combine the gochugaru, sugar, salt and pepper. Rub the mixture all over the steak, taking care to rub into every crevice.
Place the steak on a smoking hot, oiled grill or grill pan and cook for 6-8 minutes a side. The steak will still feel quite spongey even though it is cooked. It's just the way hanger steak is.
Tent the steak in foil and let rest for 15 minutes before slicing against the grain. The steak should be pink verging on red in the center, not blue.
For the Shishito Peppers
Place the peppers in a bowl and toss with the olive oil until well coated.
While the steak is resting, place a cast iron skillet on the grill to heat up. If you're not using a grill, heat the skillet on the stove until smoking. Once the skillet is hot, add the peppers and cook for 3-4 minutes, tossing every 45 seconds or so.
Remove the peppers from the heat and dress them with a drizzle of sesame oil and a sprinkling of salt.
Place the dressed peppers on a platter along side the sliced hanger steak and pickled daikon.