RIKUZENTAKATA, Japan—It was not until late May—several weeks after rescue workers had discovered the remains of his wife in the ruins here—that Mayor Futoshi Toba began to focus on the future.

In the immediate aftermath of the earthquake and tsunami that swallowed this city on March 11, the mayor hadn't had time to plan far ahead. The disaster wiped away the city's downtown, killed almost a 10th of its 23,000 people, and flattened the local economy. The waves destroyed Mr. Toba's home and took his wife, Kumi, leaving their...