In a bowl, mix together the boar meat, ⅔ cup panko, egg, onions, ginger, soy sauce, salt, and red pepper flakes until just combined. Don’t overmix. Form the meatballs with rounded tablespoon-size portion of the mixture and place on a parchment paper–lined baking sheet. Refrigerate for a few minutes to firm up the meatballs. If they seem too soft, work in a few more breadcrumbs.