Living by the sea, protecting the sea, and journeying across the sea…They’re the BLUE MERMAIDS! Because of a shift in tectonic plates around 100 years ago, Japan lost much of its area to submergence. To preserve Japan’s territories, Coastal Cities sprung up, one after the other. Eventually, they became Marine Cities, and along with the expansion of sea-lanes to connect them, the need arose for a sizable staff to protect the seas. At the same time, maritime jobs were becoming more popular among women. Hence, the BLUE MERMAIDS had become every female student’s dream job.
O enredo deste filme se passa 30 anos após a série original. Quando um meteoro está prestes a se aproximar da Terra, Summer Adams, Cole e Bruno se encontram e trabalham juntos para impedir a invasão de Onimaro com o poder de um novo Yo-kai Watch e Yo-kai que pode mudar entre as formas Lightside e Shadowside. . O filme em si serve como prólogo para o anime Yo-kai Watch Shadowside, que estreou alguns meses após a estreia do filme no Japão.
