Lay the chicken breasts out between 2 sheets of plastic wrap and beat to 1cm thick.
Place the soy sauce, sake, mirin, sugar and 1 teaspoon of the ginger in a flat non-metallic dish big enough to fit all the chicken in a single layer and stir until the sugar has dissolved. Add the chicken and turn to coat. Cover and refrigerate for 1 hour, turning once.
Bring a large saucepan of water to the boil. Add the rice and cook for 12 minutes, stirring occasionally. Drain. Stir in the chives and the remaining ginger, then cover until ready to serve.
Meanwhile, drain the chicken, reserving the marinade. Heat the oil in a large, deep frying pan and cook the chicken, skin-side-down, over medium heat for 4-5 minutes, or until the skin is crisp. Turn and cook the other side for 4 minutes, remove from the pan (the chicken should be not quite cooked).
Add the reserved marinade and 1/4 cup water to the pan and scrape up any sediment. Bring to the boil over high heat, then return the chicken (skinside up) with any juices to the pan. Cook for 5-6 minutes, or until just cooked, turning once to coat.
Divide the rice among four plates and place the chicken (either whole or sliced on the diagonal) on top. Drizzle with a little sauce, and serve with steamed Asian greens.