Looking for a specific manga

I am looking for a shojo manga, it starts by somehow having a girl (high school age I think) somehow get into a strange new world where she ends up saving this super powerful demon from the "good" guys. Throughout the story they fall in love and take down a corrupted orginization (can't remember if it is a church or the government) The girl may or may not have powers, can't remember. The demon is tall, black hair... The first time they meet is in a large forest... If anyone can help, please let me know. Thank you!