Heat the oven to 425°F and oil a rimmed sheet. Mix panko with milk, then gently fold in beef, pork, egg, ginger, garlic, salt and pepper. Shape 24 meatballs and bake for 16 to 20 minutes until the centers reach 160°F.
Meanwhile, simmer grated pear, gochujang, soy sauce, vinegar, brown sugar and broth in a saucepan for 3 minutes, stirring until combined. Transfer hot sauce and hot meatballs to a 4-quart slow cooker.
Cover and cook on HIGH for 2 hours, turning gently once. Whisk cornstarch with slurry water, fold it into the sauce and cover on HIGH for 15 to 20 minutes until thickened and meatball centers reach 165°F.
During the final half hour, bring rice and rice water to a boil in a saucepan. Cover, reduce to low and cook for 18 minutes, then rest off heat for 10 minutes.
Turn off the cooker and stir sesame oil gently through the sauce. Divide rice among 6 bowls and add 4 meatballs and sauce to each serving.