It was created to capture women on Namegawa Island to be scientifically altered into Marinian-like beings to serve the Fuuma, capturing Dr. Koshirou and Yoko as a result. However, a prototype gillman leads Dai to their base of operations before being killed off. Freeing the Fuuma captives, Shaider pursues Umiumi to the Fushigi Dimension. Fighting the monster's giant sharks and phantom-masked grunts, Shaider destroys Umiumi with Shaider Blue Flash. Its powers include swimming, a zambatou, size changing, summoning six gilled sharks, dividing into three swordsmen and teleportation.