An American transfer student of Osaka High with a mission.
In a past visit to Japan, Mizuki Ashiya was nearly kidnapped until Izumi Sano saved her, but caused his foot injury thanks to the thugs. Mizuki felt wholly responsible for Izumi's absence to high-jumping, so one day, she dressed up as a guy and enrolled herself into Osaka High in order to persuade Izumi into high-jumping again. However, after her enrollment, she gets into one mishap after another thanks to her schoolmates.
Despite the many obstacles she faces in Osaka High, Mizuki is determined of her goal and can be a sweetheart at most times, even when hiding her true identity.