In the waters off Hokkaido Prefecture, in Japan's far north, a number of mysterious natural phenomena have been observed in recent years. Echoing the secret truth of an ancient Ainu proverb, the winter sea is transformed into a white expanse overnight, covering several kilometers of coastline. Elsewhere, a large whirlpool suddenly appears in the sea, as if out of nowhere, hinting at a surprising spectacle in the depths; and in a bay off the Sea of Okhotsk, a vast battalion of shellfish appears to march across the seafloor. Employing cutting-edge underwater camera technology, our specialist crew set out to investigate these intriguing oceanographic events.