In a bowl, combine soy sauce, mirin, sugar, minced garlic, and sliced scallions.
Mix well to ensure all ingredients are combined.
Place the ribeye steaks in the marinade and ensure they are fully covered.
Let them marinate in the refrigerator for at least 2 hours.
Preheat your grill to medium-high heat.
Lightly oil the grill grates.
Remove the steaks from the marinade and discard it.
Season the steaks with salt and pepper on both sides.
Grill the steaks for 4 to 6 minutes on each side for medium rare.
Let the steaks rest for about 3 minutes before slicing.
Add grilled lemon halves for squeezing over the steak.