The battle between the two Ultra Brothers and Saki Mitsurugi, who transformed into a kaiju, was long and hard with no clear winner. But shortly afterwards, Saki visits the two brothers at Quattro M! Although Katsumi proposes that they all work together to save the world from destruction, Saki refuses to respond, and instead begins to tell them the story behind their mother, Minato Mio’s disappearance! And an inescapable, centuries-old battle will start once again…