Tatsuya and Miyuki receive a new assignment from the head of the Yotsuba family. And although at first glance it looks more like a vacation than work—they have to go to Okinawa to symbolically attend a memorial service, while the Okinawan beaches and sunshine will be entirely at their disposal—this is only a cover. Around the same time, an official reception is planned in honor of the completion of building an artificial island, an economically important national project. And the Yotsuba family has information that the event will be sabotaged…