In a mixing bowl, combine chicken thighs with soy sauce, gochujang, gochugaru, sesame oil, minced garlic, grated ginger, brown sugar, and black pepper. Stir well and refrigerate for at least 30 minutes.

In a large pot, pour in chicken broth and water. Add soy sauce, mirin, sake, and sesame oil. Add kombu, shiitake mushrooms, green onion whites, ginger slices, and garlic. Simmer for 30 minutes to 1 hour.

Carefully remove kombu and shiitake mushrooms. Strain the broth into a clean pot, discarding solids. Keep warm over low heat.

Heat oil in a skillet over medium-high heat. Cook marinated chicken for about 3-4 minutes per side until browned and cooked through. Slice into strips.

In a separate pot, boil salted water. Add fresh ramen noodles and cook according to package instructions, about 3-4 minutes. Drain and rinse under cold water.

To assemble, divide noodles among bowls, ladle hot broth over them, and top with sliced chicken, halved soft-boiled eggs, bean sprouts, corn, and kimchi. Garnish with sesame seeds, nori, and chili oil if desired.