Cut the tuna into bite-sized pieces.
Finely chop the green onions and onions.
In a bowl, mix soy sauce, water, sugar, cooking wine, minced garlic, and black pepper to make the marinade.
Put the chopped tuna and vegetables into a container, pour in the marinade, and make sure everything is submerged.
Add sesame oil and yuzu syrup, then mix well.
Let it marinate in the refrigerator for at least 2 hours.
Serve the marinated yuzu tuna in a bowl.