Chicken Heart Yakitori Skewers

Name: Chicken Heart Yakitori Skewers
Ingredients: 3/4 cup sake; 1 1/2 cups high-quality soy sauce, such as Kikkoman Smooth Aromatic; 3/4 cup sugar; 1 teaspoon Chinese chicken powder; 3 scallions, trimmed and sliced into large pieces; One 3-inch piece fresh ginger, cut into large pieces; 2 pounds chicken hearts, valves removed and hearts cut in half; 2 bunches scallions, whites only, cut into 1 1/2-inch-wide pieces; 1/2 cup each iodized salt and black pepper, combined in a shaker; Sansho and shichimi pepper, for garnish