Kwazii and Dashi become entangled in a strange deep-sea creature - a siphonophore - and when a geyser blasts it toward the surface, the Octonauts must stop its ascent before it fatally bursts.
故事將圍繞綠谷出久與死柄木弔的對峙、轟焦凍與其兄轟燈矢了斷家族恩怨,以及麗日御茶子與渡我被身子的相遇展開,同時也將迎來歐爾麥特與「人人為我」的戰鬥結局。
故事承接《鬼灭之刃 柱训练篇》。