Rinse the flanken-cut beef short ribs under cold running water and pat them dry with paper towels.

In a medium bowl, combine soy sauce, brown sugar, mirin, honey, sesame oil, minced garlic, grated Asian pear, grated onion, and black pepper. Whisk until the sugar dissolves.

Place the ribs in a large resealable plastic bag or shallow dish, pour the marinade over the beef, ensuring it's well coated. Seal tightly and refrigerate for at least 4 hours, preferably overnight.

Preheat your grill to medium-high heat, around 400°F (200°C).

Remove the ribs from the marinade, letting excess drip off. Place on the hot grill and cook for 3-4 minutes per side until a caramelized glaze forms.

Transfer grilled ribs to a serving platter and garnish with green onions and sesame seeds. Serve with steamed rice and side dishes like kimchi.