Very simple marinade for the tuna. The most important part to prepare this is a VERY hot pan or grill.
Marinade the tuna in soy, mirin, honey and wasabi for about an hour. Coat it with sesame seeds. Sear for 15 to 30 seconds per side or to desired temperature. Remove to rack and rest for 3 minutes. Cover with foil or plastic wrap to achieve carry over cooking. Slice thinly and serve with the dipping sauce.