Tadashi, a member of the arcadia crew, is kidnapped by ships from Tokaga, a planet enslaved by the Sylvidres. Braving the ambush set by their enemies, Albator and Arcadia dive into the underwater depths of Tokaga, and detect an emergency signal emitted by Tadashi. In front of them, the seabed is entirely covered with an infinity of wild pyramids. In one of them, a gaping hole sucks the Arcadia.