Taking place after the events of the fourth film, the series centers on Tate Adams, Summer's brother who doesn't believe in supernatural phenomena. But as he notices his sister frequently comes back home late, he decides to stalk her, only to find out she is exorcising evil Yo-kai and running a Yo-kai detective agency. With their secret revealed to him, Summer decides to let him tag along in her activities as they investigate Yo-kai crimes and take on evil Yo-kai to maintain peace all over the city. Meanwhile, Shutendoji (the one who had planned all the evil, as seen in an epilogue at the end of the fourth movie), accompanied by his Yo-kai bodyguard Doketsu, is in search of the "princess" that he has hoped to unite with, over the events of the anime. They both search for the "princess" while in their human disguises, and observing the actions of the Yo-kai detective agency.