Fifteen years after one of the world’s worst nuclear disasters, this part of the Fukushima coast feels stuck in the aftermath. Empty lots where homes once stood. Signs warning of restricted access. Convoys of construction trucks carrying radioactive dirt and materials. And then, improbably, a tour bus. Visitors are flowing into barely inhabited towns, attracted for the most part by the very catastrophe that drove their residents away. The wrecked Fukushima Daiichi nuclear plant has become a...