Salt and pepper, maybe soy.

Dry brine with salt and pepper, then add a splash of soy if you want umami.

Tuna is oily and flavorful on its own. Heavy spice blends or marinades just mask what you paid for. A dry brine—salting the steaks 15–20 minutes before searing—draws out moisture and concentrates flavor. Pepper adds a little heat. That’s it.

If you want a crust that’s more than salt, a light brush of soy sauce before the pan gives you savory depth without covering the fish. Just don’t soak it. You’re searing, not braising.

The fish does the heavy lifting.