Simmer the soy sauce, brown sugar, rice vinegar, garlic, and ginger in a small saucepan.

Stir the cornstarch with 1 tablespoon cold water until smooth, whisk the slurry into the saucepan, and cook until the teriyaki thickens. Cool slightly.

Reserve half of the sauce in a clean bowl for grilling. Toss the sliced beef with the remaining half and marinate in the refrigerator for 15 minutes.

Thread the beef ribbons onto skewers and discard their marinade.

Grill for 3 to 4 minutes per side, brushing only with the reserved clean teriyaki, until caramelized and cooked to your preferred doneness.