Momoka Sendou (nicknamed "Dragon Girl") and Ryuga Kou are childhood friends. Momoka is a martial artist, and Ryuga is a Chinese magic master who banishes demons. In order to increase his power, Ryuga calls on the spirit of a dragon to possess him, but the spirit enters Momoka instead. Now the two must unite forces and fight demons together!
Momoka is eager to give Ryuga an antique pocket watch for his 17th birthday, but the Ryuga she meets is only 13 years old! A tiny trickster fairy who lives in the watch has taken Momoka back in time, and now Momoka must find a way to return to the present day.