St. ♥ Dragon Girl

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!

(Source: Viz Media)