Like most other Asian countries, Japan does not really do “continental breakfast” so don’t expect to be dining on eggs, bacon & toast in the morning. Most food venues that will be open in the early hours of the day will be serving typical Japanese breakfasts composed of meat/fish, rice, miso soup, salad, tofu and so on. You can also find places that have set meals that will include eggs and sausages.
For those who are feeling adventurous, I recommend going to the fish market for your breakfast.
On my first morning in Japan, I headed over to the Kuromon Ichiba Market located in the Nipponbashi area of Osaka. This market is well known for its seafood offerings. Most stalls will not only sell you fresh fish & seafood but will also cook it for you to eat on the spot.
Things you can find at Kuromon include freshly cut tuna (in sashimi or grilled tuna jaw), scallops, small (baby ?) octopuses, pickled vegetables, grilled eel, sea urchin, crabs, oden and so much more.