In a bowl, combine yuzu juice, chopped scallions, soy sauce, sesame oil, salt, and pepper. Mix well to create a marinade.

Place the ribeye steaks in a resealable plastic bag or a shallow dish. Pour the marinade over the steaks, ensuring they are well coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to 4 hours for maximum flavor.

In a separate bowl, mix the softened butter, white miso paste, wasabi paste, and lemon juice until smooth and well combined. Adjust the wasabi to your preferred level of heat. Transfer the mixture onto a piece of plastic wrap and roll it into a log shape. Refrigerate until firm.

Preheat your grill or cast-iron skillet over medium-high heat. If using a skillet, add a little oil to prevent sticking.

While the grill is heating, place the remaining scallions on the grill or in the skillet. Char them for about 2-3 minutes until they are tender and have grill marks. Remove and set aside.

Remove the steaks from the marinade, letting any excess drip off. Place them on the hot grill or skillet. Cook for about 4-5 minutes on each side for medium-rare, or until your desired doneness is reached. Use a meat thermometer to check (130°F for medium-rare).

Once cooked, remove the ribeye steaks from the heat and let them rest for about 5-10 minutes. This allows the juices to redistribute.

Slice the ribeye against the grain and serve topped with the miso-wasabi butter. Garnish with charred scallions and sesame seeds, if desired.