It was invented for a 15-minute lunch break — Edo-period fishermen boiled clams, onion and tofu in diluted seawater right on their boats because they had no time for anything slower, then poured it straight over rice.
Clams are simmered in a light dashi with green onion and sometimes tofu, then poured over a bowl of rice, either as a simple simmered donburi or with the broth ladled tableside over rice at the last second.
Takoyaki (Octopus Balls)
Yakitori (Skewered Chicken)
Sapporo Miso Ramen