Make several very shallow lengthwise cuts on the inner side of each chicken thigh, so that later the chicken will be easy to roll. In a medium bowl, combine the shoyu, mirin, sake, and grated ginger. Add the chicken thighs, and marinate them for 20 minutes, turning them over several times. Remove the chicken thighs from the marinade, and wipe them dry with a paper towel.

Bring a medium pot of water to a boil, and blanch the asparagus spears for 20 seconds. Drain them, and wipe them dry with a paper towel.

Tightly roll three asparagus spears in each chicken thigh. Secure each roll with five steel, skewers, threaded through the overlapped part of the roll in a fan shape, so that you can hold all five skewers together at one end. They will form a convenient handle by which to turn over the chicken during cooking.

Heat a broiler or grill. Place the chicken rolls in a broiler pan or on the grill rack, 5 to 6 inches from the heat source, and cook the chicken rolls for 10 minutes. Turn them over, and cook them for 6 minutes on the other side. Remove the chicken rolls from the heat source. With a pastry brush, apply the teriyaki sauce on both sides of the chicken rolls. Return them to the heat source, and dry them on both sides for 1 to 2 minutes. Repeat the basting and drying process several times, until the chicken rolls are coated with a glossy layer of sauce.

After the chicken is cooked, turn the skewers to loosen them, but leave them in for 5 minutes.

In a small saucepan, warm the remaining sauce over moderate heat. Unskewer the chicken rolls, and cut each roll into 1-inch slices crosswise. Lay the chicken disks on a bed of salad greens, and drizzle the disks with a little teriyaki sauce. Sprinkle a little sansho pepper over the chicken and serve.