In a large nonmetallic bowl, add soy sauce, water, and vinegar.

Add brown sugar, white sugar, pepper, sesame oil, garlic, and onion to the mixture and whisk until the sugars have dissolved.

Place ribs into marinade and cover with plastic wrap, making sure the ribs are entirely submerged in the liquid.

Refrigerate 7-12 hours.

Preheat an outdoor grill for medium-high heat.

Shake off excess marinade from ribs and place on grill.

Discard remaining marinade.

Cook meat for 5-7 minutes per side, until the meat is no longer pink.