In a bowl, mix soy sauce, mirin, sake, sesame oil, chopped green onions, minced ginger, and minced garlic. Add the ribeye steak to the marinade, cover, and refrigerate for at least 1 hour.

Sear the Steak

Preheat a skillet over high heat. Remove the steak from the marinade, and sear for about 1-2 minutes on each side until browned. Remove from heat and let rest for 5 minutes before slicing thinly.

Ponzu Sauce Preparation

Make the Ponzu Sauce

In a small bowl, combine soy sauce, yuzu juice, rice vinegar, and bonito flakes. Mix well and let it sit for 10 minutes to allow the flavors to meld.

Sushi Preparation

Prepare Sushi Rice

Rinse sushi rice under cold water until water runs clear. Cook the rice according to package instructions, then transfer to a bowl. Mix rice vinegar, sugar, and salt in a separate bowl until dissolved, then gently fold it into the cooked rice. Let cool.

Assemble Sushi Rolls

On a bamboo mat, place a sheet of nori. Spread a thin layer of sushi rice over the nori, leaving a small border at the top. Place slices of fresh salmon or tuna, avocado, and cucumber on the rice. Roll tightly using the mat, seal the edge with a little water, and slice into bite-sized pieces. Sprinkle with sesame seeds.