In a small bowl, stir together the soy sauce, mirin, honey and sesame oil. Divide into two equal parts. Stir the rice vinegar into one part and set aside as a dipping sauce.
Spread the sesame seeds out on a plate. Coat the tuna steaks with the remaining soy sauce mixture, then press into the sesame seeds to coat.
Heat olive oil in a cast iron skillet over high heat until very hot. Place steaks in the pan, and sear for about 30 seconds on each side.