There are marinated swordfish recipes around, but the marinade liquid does not consist of "sake" only, because it doesn't have taste (no salt and/or spice). Sake is used only as supplement to enhance the flavor. Here is a simple one:
1. Make marinade sauce:
Japanese sake
Japanese mirin (if not available, replace with sake plus sugar)
Soy sauce (preferably "usukuchi" soy sauce, which is lighter brown in color)
Juice from lemon, lime, or any other fragrant citrus fruit (preferably Japanese)
--roughly 1/4 cup each (increase sauce depending on number of fish slices)
2. Marinate for 20 to 40 minutes.
3. Grill until done. (Sauteeing in a pan is also OK, although grilling tastes better.)
4. Garnish like this: