Ingredients
7 tbsp. dark soy sauce
7 tbsp. mirin
7 tbsp. sake
1 tbsp. sugar
1 1⁄2 lb. pork tenderloin, trimmed and cut into 1 1⁄2-inch pieces
1⁄2 pineapple (about 12 oz.), peeled and cut into 1-inch cubes
1⁄2 small red onion, cut into 1-inch pieces
2 tbsp. olive oil
Thinly sliced scallions, to garnish

Instructions
In a small saucepan, combine the soy sauce with the mirin, sake, and sugar. Bring to a boil over medium heat and cook until the sugar dissolves, about 3 minutes. Remove from the heat and let the teriyaki sauce cool completely. In a medium bowl, toss the pork with 1 cup of the teriyaki sauce and then refrigerate for at least 2 hours.
Light a grill. Thread pieces of pork with pieces of pineapple and onion onto wooden skewers, and then brush all the skewers with the olive oil. Grill the skewers, turning as needed and basting with remaining teriyaki sauce, until cooked through, 12 to 15 minutes. Transfer the skewers to a serving platter and let rest for 5 to 10 minutes. Sprinkle the skewers with scallions before serving.