Umibōzu

is the boss of the sea. It was used by Amachi to terrorize the Land of the Sea in the Land of the Sea filler arc. Umibozu itself is nothing more than water that has been gathered and held together by chakra, making it virtually indestructible unless it is completely evaporated. Amachi summoned it once more to defeat Naruto Uzumaki. Naruto got swallowed by its indestructable water mass and was completely immobilized, until he gained a burst of chakra from the Nine-Tailed Demon Fox and eventually broke free as it shattered into tiny droplets. Naruto got worn out as the demon fox's chakra retreated itself and fainted. After a while Naruto gained consciousness and he and his team defeated and captured Amachi. But the Sea Boss reformed and Naruto resorted to summoning Gamabunta and it was defeated by Naruto throwing an exploding tag attached to a kunai into Gamabunta's oil, completely evaporating it.