Combine say sauce, 1 teaspoons wasabi powder, 1/4 teaspoons of five-spice powder, and olive oil.
Soak tuna steaks in this for 10 minutes.
Press into a shallow pan containing bread crumbs, remaining wasabi powder, five spice powder, and sesame seeds.
The steaks should hold breading well and be placed in a cooler until you finish your beurre blanc.
Then sear to a golden finish on each side in a saute pan of extremely hot olive oil.
For the beurre blanc, combine the first five ingredients and bring to a boil.
Bring down the heat to a simmer and reduce by two-thirds.
Add cream and reduce by half, then whisk in the butter, piece by piece, until smooth and shiny.
Add soy sauce, wasabi, and salt to taste.
Serving: Place a pool of the sauce in the center of plate, cut the steaks in half on a dramatic angle to reveal the rare center of tuna, and stack upon each other, cascading down one side. Serve with your choice of sides, such as gingered carrots or a potato in puff pastry.