After Japan opened itself to the world, Japanese cooks began to adapt western dishes in their own style. For instance in the west, people use ketchup as a condiment, but the Japanese use it as a base for tomato sauces. Spaghetti naporitan was created just after World War II, after Shigetada (the head chef at the Hotel New Grand in Yokohama) saw occupying soldiers eating it. Nowadays, you can find spaghetti seasoned with soy sauce, and served with seaweed.
While living in Tokyo, we spent many evenings at Saizeriya, a cheap Japanese food chain of family-style italian restaurants. I had my very first yoshoku-style (western style) pasta there.
This is a relatively simple recipe, and uses all of my favorite japanese condiments! If you've never had yoshoku pasta, i envy you. A world of creativity awaits!