Combine chicken broth, water, miso paste, soy sauce, sesame oil, grated ginger, and minced garlic in a large pot. Heat over medium until miso dissolves, then reduce heat and let simmer.

In a separate pot, boil water, add ramen noodles, and cook according to package instructions. Drain and rinse under cold water, then set aside.

Prepare a breading station with flour, beaten egg, and panko breadcrumbs. Coat cooked chicken in flour, then dip in egg, and coat with breadcrumbs.

Heat vegetable oil in a skillet over medium-high heat. Fry breaded chicken for about 3-4 minutes on each side until golden brown. Transfer to paper towels to drain.

Divide cooked ramen noodles into bowls, ladle the broth over them, top with chicken katsu, green onions, and soft-boiled egg. Add nori sheets if desired.