Kisaki Tachikawa seems like a typical second-year middle school student, but she leads a double life as an esper. Under the guise of "Fortune Tiara," Kisaki uses her psychic powers to fight as a member of PSI—a secret defense organization that deals with extraterrestrial beings (EBEs) on Earth. Alongside her in the unit Mistress☆Fortune is her partner, Giniro "Fortune Quartz" Hashiba, who is a prodigy fighter obsessed with Kisaki's breasts. Despite his lecherous behavior, Kisaki has always been smitten by Giniro and frequently mulls over whether or not to confess to him.

When a powerful EBE appears near PSI's American branch, Kisaki is forced to transfer to assist with the fight. Even though she is vehemently opposed to being separated from Giniro, an enticing offer involving her partner causes her to reconsider the transfer. As she struggles to decide on her next step, it is unclear if Kisaki will ever make her feelings known.