Furikake is an essential Japanese seasoning that comes in endless variations, but the flavors usually lean salty, earthy and nutty.
Trim 4 scallions, then halve lengthwise. Heat 1 tbsp. oil in heavy skillet over high. Add scallion halves and cook, stirring often, until charred, about 4 minutes. Transfer scallions to a plate. Reduce heat to medium-high. Add remaining 1 tbsp. oil to skillet. Season steak, then add to skillet. Cook, turning once, until it reaches desired doneness, about 8 minutes for medium-rare. Let rest while you make the butter. Finely chop charred scallions. In bowl, stir butter, charred scallions, garlic, furikake, and chili flakes. Slice steak against the grain; top with butter and chopped fresh scallions.