St. Dragon Girl Vol. 1 (manga)

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! A demon serpent king who appears once every hundred years to select a bride has abducted Momoka's friend Shunran. Will Momoka and Ryuga be able to defeat the demon before Shunran is lost forever?