I forgot the name but it began with a guy meeting this girl with a hime in her name, she goes into a light
but the guy follows her in there. So the girl is actually a princess in this fantasy setting marrying this prince but the guy got into the castle, and a demon appeared and attacked the guy. She marries the guy and the guy kills the demon and wakes up in a bed.....soooo anyone know this manga??

Kekkon Yubiwa Monogatari , i think