Rub salt and sugar into the chicken, then let it sit in the refrigerator for 1 hour. Meanwhile, prepare the toppings and keep them chilled.
In a medium pot, combine water, green onions, crushed garlic, and sliced ginger. Heat over medium heat until just before boiling. Add the chicken and bring to a boil. Cook for 2–3 minutes, then turn off the heat. Add the kombu, cover with a lid, and let it sit for 10 minutes, or until the chicken is cooked through.
Remove the chicken and set aside. Discard the onion, ginger and garlic. Season the broth with salt, sake, mirin, and soy sauce. Simmer for a couple of minutes, then remove from heat. Let the broth cool to room temperature, then refrigerate for 1–2 hours until chilled.
Once the chicken is cool, slice it thinly and keep it chilled.
Cook the ramen noodles according to the package instructions. Rinse them under cold running water and drain well. Cover with ice until ready to serve.
Add sesame seeds and sesame oil to the chilled broth and mix well. To serve, place the cold noodles in a bowl, pour over the chilled broth, add toppings, and serve immediately.