We were standing in the open, wood-paneled kitchen of Mirukashi Salon, a hyper-seasonal culinary retreat set in the hilly countryside of Kyushu, the southernmost of Japan’s four main islands.

At a culinary retreat on the Japanese island of Kyushu, seasonal flavors are in full bloom. Steam rolled off the copper-ringed wooden bowl and the sweet aroma of freshly cooked rice rose toward us. I ...