Cook udon noodles according to the instructions on the packaging. Drain and rinse under cold water before setting aside.
Bring a large pot of water to a boil. Add in dashi granules to the water along with dark and light soy sauce, sugar, and mirin. Bring to a simmer and let cook until the sugar and dashi have dissolved.
Divide noodles and broth between 4 bowls and garnish with green onions and seven-spice. Serve immediately.